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The Teller Mine and other German WWII Land Mines: The Hidden Danger

The Wehrmacht employed numerous types of land mines throughout the war.

This article appears in: January 2010

By Alan Vannoy

German Teller mines were insidious weapons—killing or maiming thousands of Allied soldiers and civilians. The Wehrmact employed others, too, to great effect during the Second World War. In one incident toward the end of 1944, American soldiers came across nonmetal mines in Lorraine, France. In a single minefield they found 12,000 mines made out of Bakelite or wood, which made them impossible to locate with metal detectors. By 1945, the U.S. Army in Europe recorded that mines were responsible for 2.5 percent of combat fatalities and for 20.7 percent of tank losses. (You can read more about the personal stories behind the statistics of the Second World War inside the pages of WWII History magazine.) 

German commanders considered the land mine a very effective defensive weapon and so went to great lengths to make extensive use of it. Minefields were used chiefly to cover defensive operations and retreats. In a static situation the Germans regarded minefields as an element of frontline positions, laid out according to an overall mine plan developed in close conjunction with fields of fire. German doctrine for minefield location was modified during the war so that, instead of laying dense minefields in front of the main line of resistance, as had been the practice, mines were dispersed.

Mapping the Mines

German engineers believed it necessary to survey the location of minefields and individual mines within the fields. They were instructed to choose reference points for minefields that could be identified easily, such as near a railroad grade crossing, at road intersections, or at the edge of a village.

In some instances, however, the Germans were forced to use guide wires and auxiliary fixed points. A type of auxiliary fixed point that proved practicable was the center of an equilateral triangle with sides 15 to 25 feet long. The corner points and the fixed point itself would be marked by stakes, rails, concrete or steel girders about three feet in length and connected with barbed wire. Such a fixed point could be reestablished easily after heavy shelling was received. Fixed points could also be reference points found on a map. Distances were measured in meters and azimuth readings were taken by compass.

The Germans believed it was advantageous to lay a continuous series of reference points 600 to 900 feet apart, through a division sector. These reference points would be used to determine the locations of ditches, trenches, obstacles, and pillboxes as well as minefields.

Minefield Patterns

To assure the greatest possible effect, minefields normally were laid out in patterns, but there were exceptions to this practice in sectors where the Germans did not intend to undertake offensive actions. There, they dispersed the mines irregularly in the areas between defensive positions.

The main fields or belts of antitank mines were laid in a uniform pattern with a sprinkling of antipersonnel mines at the forward edge of the field. Both types of mines might be fitted with antilifting or antihandling devices intended to cause the mine to detonate if an attempt was made to remove it, and some of the antipersonnel mines would also have trip wires attached.

In turn, a number of antitank mines would be laid at the forward edge of an antipersonnel minefield to prevent armored vehicles from detonating the main belt of antipersonnel mines. In addition, the forward edge of minefields were often sown with explosive charges placed in wooden boxes fitted with pressure fuses. These acted as both antitank and antipersonnel mines and discouraged the use of metal detectors to locate the mines.

Forward of most fields, and particularly in front of clear lanes, mines might be found widely spaced or scattered at random in unmarked groups. Mines also were laid in lines running out at right angles from the forward edge of the minefield in order to damage vehicles moving along the field in search of lanes.

Pressure-type antitank and antipersonnel mines were laid in lines. For measuring distances, a mine-measuring wire 24 meters long was used, with meter increments marked off and with five-inch-diameter rings on the ends of the wire. This measuring wire, in addition to measuring the distance between fixed points, served to lay out right angles by staking out a triangle with sides of six, eight, and 10 meters, respectively. Spaces between mines were determined by reference to the marks on the wire and four rings on one end used to set rows.

The density of a minefield depended on the interval set between mines and the number of rows used. Clear lanes were left open for patrols to transit, and passage lanes for assault troops. New lanes were set periodically and old ones closed.

Mine belts were normally laid in sections of 80 by 105 feet. The sections usually were staggered, and, for extensive mine belts, combined in units of three or four to form forward or reverse arrowheads, or echelons.

Defending the Approach and the Retreat

The Germans emphasized that minefields were to be covered by fire, although during a hasty withdrawal they often did not follow this principle. It was common for a minefield to have a listening post with two men at the rear edge; about 70 or 80 yards to the rear a covering party of four or five men was placed with one or two light machine guns.

When the Germans were conducting a hasty withdrawal, they usually laid a large number of small nuisance mines and minefields. These fields contained many different types of mines, which often were unmarked and showed evidence of being hurriedly laid. The lack of pattern uniformity made detection and clearing laborious and dangerous.

Mines were also laid close to or on roadways, on airfields and railways, and along telegraph and telephone lines. Hard-surfaced roads were usually avoided in the case of hastily laid mines, but khaki-painted antitank mines sometimes were placed on the surface at dips in the road in the hope that drivers would be unable to avoid them. The Germans also placed mines along the shoulders of a road opposite narrow places where drivers might have to swing wide to pass and at the entrances to defiles where they had to pull off the road to wait for vehicles moving in the opposite direction. Other places usually sown with antitank mines were turnouts, sharp bends, and well-worn wheel ruts.

Placement Ingenuity

The Germans attempted to make their mines difficult to detect. They buried them as much as 24 inches below the surface so that they would explode only after a number of vehicles had compacted the earth sufficiently to set off the fuse. They placed explosives in wooden boxes to prevent discovery by mine detectors, and they made tire prints in the soil over the mine by drawing a detached axle and wheels over the mine.

They showed considerable ingenuity in setting antipersonnel mines randomly on the line of a possible enemy advance. Road demolition areas were sown with antipersonnel mines, and kilometer marker posts at points where drivers would have to dismount to read directions were similarly treated. Mines also were placed in ditches, often close to the tripwire peg of another mine.

Nuisance fields were closely spaced, occasionally so close as to cause sympathetic detonation. This was particularly possible when mines were laid with their pressure plates almost flush with the surface of the ground and only lightly covered with earth.

The Germans also set dummy minefields. These took various forms. In some cases a trip wire was laid to give the appearance of a minefield perimeter wire, with the usual lanes and the ground disturbed at regular intervals. Scrap metal, often dispersed with real mines, was placed in shallow holes to cause a reaction by mine detectors. Dummy mines were often connected to live booby traps.

Marking Mines

The Germans stressed the marking of minefields and attempted to mark them in such a manner that they could not be recognized by the enemy but could easily be found by their own troops. Initially, the methods of marking minefields were not uniform. The front edge of a field was often unmarked. Because of many accidents caused by friendly minefields, the Germans issued orders making proper marking mandatory.

Typical examples of markings included the placing of a single knee-high wire, use of cattle fencing, placing of empty mine crates, and signs. Marking stakes were also used to indicate minefields. The stakes were flat on one side for a length of about eight inches, with the flat surface painted red and the letter M ( Minen ) in black. Such stakes were used only on the friendly edges of minefields.

Signs were painted in red and white on boards or pieces of sheet metal and fastened to two stakes. The edges of minefields were indicated with signs marked with horizontal stripes. Edges of lanes through the fields were indicated by vertically divided signs, with the white portion on the side of the lane (safe) and the red portion on the side of the minefield (danger). The reverse sides of the signs, the sides toward the enemy, were painted olive drab. If red paint was not available, the Germans substituted black and white signs. These were painted with the words Minen (mines), Gasse or Gassen (mine lanes), and Entimint (an area cleared of mines). Minefields were indicated by vertical lettering, dummy minefields with slanted letters. This distinction, however, was supposed to be made known only to German engineers because it was feared that other troops, if taken prisoner, might divulge the locations of dummy minefields.

The Germans were methodical not only in laying mines but in planning and recording minefield information. Mine plans provided technical details on one or more fields. A mine map showed all mine obstacles within a sector and their tactical significance, but without technical details.

A mine map usually showed the name of the obstacle (minefield) and designation of the unit that laid it, the name of the area in which the obstacle was located, a grid reference, the obstacle shown in a small sketch in red, the date the minefield was laid, and the name and rank of the officer or noncommissioned officer in charge of laying the field.

Data on the mines used included the number, type, and fuse; whether the mines were dug in; the number of rows, and number of mines per row; any information about fences; and information about special features that distinguished the field.

Minefield type identification was indicated by colored lines drawn diagonally across the upper right corner of the mine map, identifying the type of minefield. A red diagonal line designated fields that could not be cleared because some or all the mines were booby-trapped; a yellow diagonal line designated fields that could be cleared by using data from a mine document; a green diagonal line designated dummy minefields; and mines taken up or exploded were marked in red. The number of the minefield plan and unit designation appeared on the upper right corner of the plan.

A drawing of the minefield was included, using a scale from 1:500 to 1:2,000. Other information included the shape and size of the field, its pattern, the location of booby-trapped mines, the location of survey points with azimuth and distances, the location and type of any warning fence, the location of front lines and fortifications, neighboring minefields, mine lanes, terrain features, and any special features.

Minefields in the Army’s Organizational Structure

Mine plans were provided to company or battalion command posts—with copies distributed to the engineer company that was in charge of the minefield, to the division, to the army, and to a central file at Dessau-Rosslau.

Engineers provided frontline troops with instructions or sketches with the approximate location and extent of minefields. These sketches, as a rule, did not contain details on types of mines or fuses or on minefield patterns.

Army headquarters usually designated certain areas for fields of scattered mines. In such a case, mine reports took the place of mine plans. Normally, mine reports contained the number of the order authorizing scattering of mines, the designation of the units scattering the mines, the name and number of the field containing scattered mines, the map location of the scattered minefield, the number of mines scattered by types and fuses, and the number and type of booby-trapped mines and kinds of booby traps.

“Bouncing Betty”: The S-Mine

The Germans entered the war with just two types of antitank mines and one type of antipersonnel mine. By the end of the war they had 16 different types of antitank mines and 10 types of antipersonnel mines, and they employed many different types of booby traps or improvised devices. From 1942 on they placed increasing importance on the mine as a weapon of attrition.

The S-mine (Schrapnellmine), also known as the “Bouncing Betty,” was the best-known version of a class of antipersonnel mines referred to as bounding mines. When triggered, these mines were launched into the air and then detonated at about waist height. The explosion released a lethal blast of steel balls and steel fragments in all directions. Developed in the 1930s, the S-mine was used extensively during the war. It was designed for use in open areas against unshielded infantry. Two versions were produced, designated by the year of their first production: the SMi-35 and SMi-44. There are only minor differences between the two models. More than 1.93 million were produced.

French troops first encountered the S-mine in the German Saar in September 1939. The French nicknamed the mine “the silent soldier.” Germany used the S-mine heavily during defensive operations later in the war.

The S-mine was a steel cylinder less than 13 centimeters (five inches) tall, without its sensor, and only 10 centimeters (four inches) in diameter. A steel rod protruding from the mine’s top held the main fuse, where its trigger or sensor was attached. The SMi-35 had a central fuse, while the SMi-44 had an offset fuse. It weighed approximately four kilograms (nine pounds).

The main explosive charge of the mine was TNT; the propelling charge was black powder. The standard pressure sensor was ignited by a percussion cap.

The main fuse was designed to delay the firing of the propelling charge for approximately four seconds after the mine was triggered. The explosion of the propelling charge sent the mine upward into the air and activated three short-delay pellets between the propellant charge and the three detonators. These pellets delayed the mine’s detonation long enough for it to reach a specific height before exploding.

The standard pressure sensor was designed to activate if depressed by a weight of roughly seven kilograms (15 pounds) or greater. This was to ensure it was not set off by wildlife. A trip wire adapter for the mine used a shallow Y-shaped device and would trigger the mine if the trip wire was pulled away from the mine.

The S-mine was normally triggered by a three-pronged pressure fuse. It could also be modified to be triggered by a trip wire or could be triggered manually.

The time between triggering and ignition of the propelling charge varied between 3.9 and 4.5 seconds, depending on the age and condition of the mine. According to German documentation, the S-mine was lethal within 20 meters (22 yards) and could inflict casualties within 100 meters (110 yards). A common misconception about the S-mine was that it would not detonate until its victim stepped off the trigger. The mine would detonate whether the trigger was released or not. The most effective way to survive the mine’s detonation was not to flee but to fall to the ground lying face down as quickly as possible.

The S-mine was constructed mostly of metal, so it could be easily located by metal detectors. The mine could also be detected through careful manual probing, a time-consuming process. It was important to probe at an angle that would not accidentally depress the pressure sensor.

Once an S-mine was discovered, disarming it was fairly simple. To prevent triggering while the mine was being planted, the pressure sensor featured a hole where a safety pin kept the sensor from being accidentally depressed. This pin was removed once the mine was planted. If the discovered mine was fitted with the pressure sensor, the personnel disarming it would slip a pin into this hole. If the device was armed with a trip wire or electrical trigger, this could simply be cut. The Germans were known to use booby traps to discourage this, so caution was advised. The mine could then be removed carefully from the ground and the sensor easily unscrewed.

Non-Metal Anti-Personnel Mines

The Schu-mine 42 was a model of an antipersonnel blast-type mine. It consisted of a simple wooden box with a hinged lid containing a 200-gram block of cast TNT. A slot in the lid pressed down on the striker retaining pin, and sufficient pressure on the lid caused the pin to move, releasing the striker that triggered the detonator. The mine was cheap to produce, and its wooden body made it difficult to detect.

The Glasmine 43 was another antipersonnel mine. To make the mine less detectable, the entire body was made from glass. Initially, only mechanical igniters were used, but later models had chemical igniters. However, the Glasmine 43 was not produced in large numbers.

The History of the Teller Mine

The Teller Mine (or T-mine) was a German antitank mine developed between the wars. The Teller mine 29 was a round metal-cased antitank blast mine. It first entered service in 1929. Although replaced by later models, this model did see limited service, notably after D-Day in France, where Allied troops reported encountering it. The mine used a pressure or a trip wire fuse. It was also fitted with two secondary fuse wells that enabled the fitting of antihandling devices.

The Teller mine 35 (T.Mi.35) was used extensively during the war. The mine was made of sheet steel and had a slightly convex pressure plate on the top with a central fuse well. It also had a fuse well on the side and bottom for anti-handling devices. For use on beaches and under water, the mine could be deployed inside an earthenware or concrete pot that acted as a waterproof jacket.

The Teller mine 42 (T.Mi.42) was a metal- cased antitank blast mine. Based on the Teller mine 35, it had an improved resistance to blast because it was smaller than the 35.

The Teller mine 43 was a circular, steel-cased, antitank blast mine. It was a modified version of the Teller mine 42 that used simpler production techniques. Between March 1943 and the end of the war, over 3.6 million Teller mine 43s were produced.

The Teller mine was designed with a circular casing rising toward the center, where a large, flat pressure plate was located. A rectangular metal carrying handle was fitted to the side of the mine. The pressure plate sat over the fuse well. At the bottom of the fuse well was a booster charge, surrounded by a doughnut- shaped main charge of 5.5 kilograms of TNT or Amatol. The mine had secondary fuse wells on the side and base to enable antihandling devices to be fitted. Additionally, it could be fitted with an antitampering device, detonating the mine if the pressure plate was lifted. The mine could also be fitted with a tilt rod fuse, screwed into to the side fuse well.

In contrast to the “dinner plate” mines like the Teller mine were “bar mines” such as the Riegel mine 43 or Sprengriegel/R.Mi. 43. Its long narrow body was designed to increase the probability of a vehicle triggering it. Made of steel, the mine had a thin, oblong shape (800 millimeters) and consisted of lower and upper metal trays and an explosive block of four kilograms of TNT. It used two fuses inserted into either end of the block although it could be used with an additional top pressure fuse. More than three million were produced between 1943 and 1945. The mine was almost impossible to disarm since corrosion of the wires in the fuse made it sensitive to touch. In addition, the mine could be fitted with up to three antihandling devices.

Mine Innovations

Possibly the most advanced German antitank mine of the war was the minimal metal Topfmine. The Topfmine was a circular, minimum metal antitank blast mine that entered service in 1944. The mine was in a case made of compressed wood pulp, cardboard, and tar along with glass plugs and components designed to be undetectable by Allied mine detectors. Often the only metallic part of the mine was the detonator.

To enable the mines to be found by friendly forces, they were painted with a black sandy substance called Tarnsand. Allied forces found that although the mines were undetectable by Allied mine detectors, German mine detectors could locate them. After the war Tarnsand was discovered to be mildly radioactive, permitting the German mine detectors, which incorporated a simple Geiger counter, to locate them.

The Panzer-Stabmine 43 antitank mine, together with the Hohl-Sprung mine 4672 (hollow-charge jump mine), was the first mine to combine a shaped charge warhead with a tilt rod detonator. A Panzerfaust warhead was mounted in a metal holder on a wooden panel, which was buried with a rod protruding above the ground.

When a vehicle passed over the mine, the rod was forced sideways, triggering a black powder charge at the base of the projectile, launching it out of the ground and into the belly of the passing vehicle. The 125mm warhead’s 1.6- kilogram shaped charge could penetrate over 100mm of armor and was capable of destroying most tanks. However, the mine was not issued until January 1945, due to manufacturing problems. Only 59,000 were produced because it was felt that the warheads were better employed as antitank handheld rockets.

A Legacy That Kills

During operations in North Africa, many large minefields were put down as barriers. In time many of these locations went unmapped, and markers were lost or covered with drifting sand. Even today, the Red Cross estimates that over 27 percent of Libyan farmland is unusable due to World War II minefields. In Europe, minefield clearance is still being undertaken in the Netherlands and France. Although the war ended more than six decades ago, its legacy is still with us in the form of these deadly devices.

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The Truth About Tripwires: Why Small Force Deployments Do Not Deter Aggression

Dan Reiter , Paul Poast PDF Download -->

A pillar of American grand strategy since 1945 has been the deployment of forces — sometimes smaller and sometimes larger — abroad. A key logic underpinning smaller deployments is that they serve as tripwires: Attacking them is assumed to inevitably trigger broader intervention, deterring aggression. We question this logic. Not only are small tripwire deployments unlikely to prevent an attacker from capturing its objective and establishing a strong defensive position, tripwire-force fatalities may be insufficient to provoke broader intervention. To deter, forward deployments must be sufficiently substantial to shift the local balance of power. Our claim is examined in three 20th-century deterrence attempts: the successful 1949 American attempt to deter a North Korean attack on South Korea; the unsuccessful 1950 American attempt to deter a North Korean attack on South Korea; and the unsuccessful 1914 British attempt to deter a German attack on Belgium.

Basing U.S. troops close to the front lines of an area where war is likely to break out has been a cornerstone of American grand strategy since World War II. 1 From the demilitarized zone between North and South Korea to the plains of West Germany during the Cold War, U.S. troops have been placed directly in the path of expected assaults. The goal of forward-deploying these troops is simple: to deter aggression. Mere verbal promises to protect an ally can be dismissed as “cheap talk.” 2 Making an effective threat to protect an ally requires non-verbal measures. After all, actions speak louder than words.

The United States has sometimes sought to achieve deterrence on the cheap through the deployment of smaller “tripwire” forces. While tripwire forces are too small to shift significantly the local balance of power, the idea is that such small deployments can still boost deterrence by increasing the likelihood of American intervention. According to this approach, the deaths of these troops in the early stages of fighting would compel a larger military response because, if America’s leaders were to do nothing in response to those deaths, they would be punished at home and the country would suffer damage to its international reputation. Thus, tripwire-force deployments boost deterrence by increasing credibility.

However, we argue that the deterrence benefits of tripwire-force deployments are exaggerated. These forces will not boost deterrence for two related reasons. First, tripwire deployments do not, in reality, significantly increase the credibility of the deterrent threat. The deaths of troops in combat will not necessarily create a strong public motive to intervene in order to seek revenge or protect a country’s reputation, even given the prospects of broader casualties. Second, even if the deaths of such troops could create these motives to intervene, potential attackers could strike anyway in order to achieve a fait accompli and create a strong defensive position.

In contrast to tripwire forces, the deployment of a larger contingent of troops can actually boost deterrence success. If forward-deployed forces are sufficient to shift the local balance of power, potential attackers will be less confident that they can succeed and less confident that they can achieve a fait accompli before reinforcements arrive. As a result, potential attackers will be less likely to actually launch an attack.

After presenting these general arguments below, we apply them to three empirical cases. We demonstrate that North Korea elected not to attack South Korea in 1949 because of the substantial deployment of U.S. troops to South Korean territory. On the other hand, the deployment of a small American tripwire force to South Korean territory in 1950 failed to deter a North Korean attack. Finally, we argue that, had Britain deployed a sufficient body of troops to Belgium before the July 1914 crisis, Germany would have been deterred from attacking Belgium and escalating the Austrian-Serbian crisis, permitting World War I to be avoided.

Understanding the logic and effectiveness of both tripwire and more substantial deployments is highly relevant to contemporary foreign policy debates. For example, during his presidency, Donald Trump consistently complained about the costs of deploying U.S. troops to allied territories and threatened to reduce American troop deployments abroad. 3 Or, consider NATO’s Baltics intervention plan, discussed below, which some consider to be essentially a tripwire plan. In 2018, the United States deployed a small number of marines to Taiwan ostensibly to protect diplomatic personnel there. But observers noted that these troops could serve only as a tripwire in the event of a Chinese invasion. 4 Strong faith that the deployment of a small tripwire force significantly bolsters deterrence could push President Joe Biden, who is eager to cut defense spending to both address domestic needs and decrease the deficit, to reduce U.S. troop deployments abroad, especially in South Korea, under the assumption that a smaller force would be sufficient to trigger America’s involvement in a conflict there and deter aggression. 5

The U.S. government should stop assuming that undersized tripwire-force deployments have outsized deterrence effects. If a state is going to commit troops to deter aggression, it should do so with the understanding that the troops being deployed ought to be able to shift the local balance of power on their own. When it comes to forward troop deployments, more is better.

Tripwires and the Hope of Deterrence

In order to prevent attacks on other states, some states make deterrent threats against potential attackers. A core tenet of deterrence theory is that such threats are more likely to succeed if the potential attacker believes the defender has credibility — the willingness to execute the threat — and the capability — the ability to carry it out. 6 Throughout the development of deterrence theory, scholars and policymakers have paid considerable attention to the credibility part of the deterrence formula, but less attention to the capability element.

Within the U.S. alliance network, tripwire forces have been seen as necessary for boosting deterrence, because alliance agreements alone are not viewed as sufficient to deter an attack. One reason is that alliance treaties frequently contain loopholes and conditions that enable states to find a legal justification not to intervene if an ally is at war, or to offer only very limited assistance. 7 Indeed, the United States deliberately included a number of loopholes in its post-1945 treaties, such as the North Atlantic Treaty, including restricting the geographic purview of some treaties, giving signatories the ability to decide what level of intervention would be appropriate, and requiring intervention only if Congress formally declared war, among others. Politicians might be able talk their way out of the obligations of an alliance treaty, as France did when it abandoned Czechoslovakia in 1938, but, it was argued, abandoning Americans who had been killed in battle by hostile forces would be much more difficult.

Within the U.S. alliance network, tripwire forces have been seen as necessary for boosting deterrence, because alliance agreements alone are not viewed as sufficient to deter an attack.

Credibility was the central question of Thomas Schelling’s famous 1966 book, Arms and Influence . How could defenders like the United States credibly signal their willingness to go to war on behalf of their allies? Schelling suggested deploying tripwire forces to the territory of the potential target. A tripwire force is defined as a body of troops that is not large enough to shift the local balance of forces in order to stop or significantly slow down an attack. Schelling’s main claim is that the presence of such a force makes a threat to intervene more credible, because the early and unavoidable deaths of friendly troops in combat would force defender intervention. As Schelling famously wrote of the American tripwire force sent to Berlin,

The garrison in Berlin is as fine a collection of soldiers as has ever been assembled, but excruciatingly small. What can 7,000 American troops do, or 12,000 Allied troops? Bluntly, they can die. They can die heroically, dramatically, and in a manner that guarantees that the action cannot stop there. They represent the pride, the honor, and the reputation of the United States government and its armed forces; and they can apparently hold the entire Red Army at bay. Precisely because there is no graceful way out if we wished our troops to yield ground, and because West Berlin is too small an area in which to ignore small encroachments, West Berlin and its military forces constitute one of the most impregnable military outposts of modern times. The Soviets have not dared to cross that frontier. 8

In making this claim, Schelling conflated pride, honor, and prestige to explain why setting off a tripwire would trigger an American response. 9 America’s reputation would be damaged if it did not intervene following the deaths of these forces, because it would signal a willingness to allow an enemy to overrun its allies — and even its own troops. Schelling also alludes to the possibility of a response driven by emotion — that the deaths of U.S. troops would trigger a public demand for revenge and an insistence on the deployment of American troops.

Subsequent scholarly work fleshed out, both theoretically and empirically, the credibility element posited by Schelling. Some scholars explored the possibility of making a credible nuclear deterrent threat, i.e., whether the promise of nuclear retaliation for an attack on an ally would be perceived as credible. 10 A critical component of this debate was whether long-range nuclear delivery was adequate for creating a credible deterrent threat, or if it was instead necessary for the United States to deploy tactical nuclear weapons in Europe. 11 The deployment of such weapons would both serve as a classic tripwire, in that their destruction would compel an escalatory response and create a “use-it-or-lose-it” logic — their quick destruction would mean that the weapons would be kept on a hair trigger. Some scholars maintained that a general nuclear deterrent still required conventional tripwire forces. As Glenn Snyder observed in 1961,

the point of having a trip-wire is not to show that an attack has taken place — which of course would be evident as soon as the Soviet forces crossed the border — but to implicate extra-Continental nuclear powers by means of something stronger than a treaty contract. 12

Others used game theoretic and experimental work to explore whether a threat’s credibility could be enhanced by building “audience costs,” whereby a leader is punished by an audience, typically domestic, that is displeased with the leader’s failure to fulfill a stated foreign policy promise or threat. 13 Relatedly, scholars developed the concepts of “tied hands” and “sunk costs.” 14 A government ties its own hands by raising the costs of failing to follow through on a threat. For example, it might create domestic “audience costs,” such as incurring domestic political consequences (i.e., being voted out of office) for failing to abide by a deterrent commitment. A government sinks costs by taking costly actions to demonstrate how seriously it takes the threat it is making — such as taking pricey mobilizing or arming measures. 15

Still other research has connected the desire for revenge with a willingness to support the use of force. Indeed, one survey found that, in a hypothetical scenario, a desire for revenge was a key reason that subjects were willing to support a nuclear attack against Iranian civilians following a deadly Iranian attack on U.S. forces. 16 Robert Harkavy points out that the desire for revenge goes beyond a need for “tit-for-tat” retaliation, as the latter is “devoid of much deep emotion.” 17 Instead, there is a need for retribution by righting a wrong. Harkavy was considering the perceptions of societies that had been defeated during major war, but the logic of revenge has been found to apply in other contexts, including when a country has not been directly attacked. 18

Flaws in Tripwire Logic

While the tripwire logic has been around for a long time and has compelling theoretical attributes, it has two interrelated flaws. First, potential attackers might not see the motives to avenge a tripwire force as increasing the motive to intervene. Second, the temptation of a fait accompli might encourage aggression even if reputation and revenge create motives for a defender to intervene.

Regarding the first critique, it is incorrect to assume that all individuals (in or out of government) place a high value on reputation, honor, and revenge, especially in relation to other priorities and values. 19 Indeed, a large segment of the population might have a distaste for the use of force and, hence, would punish a leader for even making a threat (but also reward that leader for backing away from the threat). 20 Critics of the audience-cost proposition have observed that publics and governments may be willing to accept the reputational costs of failing to execute a deterrence threat if failing to execute undermines other important values, such as a desire to avoid entering difficult to win, costly wars over dubious stakes. 21 Publics may put a higher value on consistency in policy, especially if consistency means staying out of conflict. 22 Emphasis on reputation and revenge is not strong across all populations. Studies have found that the willingness to demand revenge and defend the national reputation and honor varies interpersonally and across subnational cultures. 23

Further, leaders have the ability to shape the degree to which publics perceive harm to national honor for backing down from a threat. According to some surveys, presidential rhetoric can significantly reduce the audience costs that would otherwise be imposed for backing down. 24 This is also the case for revenge. In her careful study of the connection between revenge and support for war, Rachel Stein notes that

it is not the case that a highly vengeful public will seize upon the slightest provocation to demand war from a reluctant leader. Rather, broad public endorsement of revenge is a latent source of support for war that leaders can activate by deploying strategically crafted rhetoric. 25

Thus, motivated leaders can avoid war even after tripwire troops have been killed.

A leader’s rhetoric aside, the human and financial costs of intervention counterbalances the public desire to intervene for the sake of reputation or revenge. Desiring revenge, or to salvage one’s reputation, does not cause individuals to ignore the costs of war. There is an extensive body of scholarship on the sensitivity of democratic publics toward casualties, and specifically how this sensitivity affects the public willingness to support the use of force. Research on protracted wars has demonstrated persuasively that support for war declines as casualties mount. 26

There is less work on how casualties affect the willingness of the American public to support intervening with force. Anecdotally, there are episodes of casualties failing to inspire demands for broader intervention. Casualties suffered by American peacekeeping troops in Beirut in 1983 and Mogadishu in 1993, for example, did not spark a public demand for broader intervention, and indeed, in both cases, American forces were eventually withdrawn without triggering a public backlash. 27 Similarly, although several American vessels were attacked by German submarines in the Atlantic Ocean in 1941 before America’s entry into World War II, none of those attacks were sufficient to motivate the country’s entry into the war or retaliation against Germany. As late as October 1941, two American destroyers were attacked, killing 126 Americans, and still there was no public outrage and President Franklin Roosevelt did not order any retaliatory action. Meanwhile, naval recruitment dropped 15 percent, suggesting that concern over becoming a casualty at sea in clashes with German submarines exceeded demands for revenge. 28

A leader’s rhetoric aside, the human and financial costs of intervention counterbalances the public desire to intervene for the sake of reputation or revenge. 

A few surveys have looked for tripwire effects by asking participants whether they would be more likely to support intervention if friendly forces suffered serious casualties. The results have been mixed. Some surveys have explored this question in the context of audience-cost theory, asking participants whether, if a leader were to make a threat and then back down, that leader would earn higher levels of disapproval if friendly forces had been killed. Michael Tomz’s research presented participants with scenarios in which a country attacked a neighbor and the U.S. president threatened to push out the invaders but then did not take that action. He found that subject disapproval of the president was higher when they were told that 20 Americans had been killed in the initial fighting. 29 Similarly, Graeme Davies and Robert Johns found that, when British subjects read about a scenario in which a terrorist group captured British soldiers and the prime minister threatened to take action but did not, their disapproval was higher when they were told of the deaths of four British combat pilots. 30 Only one survey experiment has more directly explored for tripwire effects in public opinion by asking respondents to consider scenarios where troops were forward deployed. In their series of surveys on an array of different conflict scenarios, Paul Musgrave and Steven Ward found tripwire effects to be contextually restricted, substantively limited, or non-existent. 31

What about international audience costs? Might the prospect of damaging their countries’ international reputation push governments to rescue embattled friendly troops? Some of the reasons why the prospect of domestic audience costs fails to deter are also reasons why the prospects of international audience costs fail to deter. If aggressors believe that a defender’s public is highly sensitive to casualties and wishes to avoid them, then the aggressor may come to believe that the defender will not approve broader intervention even at the risk of damaging its international reputation. 32 Aggressors may also see hesitant defender governments as motivated to use treaty loopholes and framing to reduce the international audience costs of deciding against broader intervention.

The Fait Accompli

Regarding the second critique, even if aggressors sometimes recognize that killing an ally’s troops will motivate that ally to intervene to protect its reputation or enact revenge, the prospect of a fait accompli may tempt them to attack anyway. 33 A fait accompli is the rapid conquest of territory and defeat of tripwire forces before reinforcements can arrive. Current scholarship proposes that attackers are tempted to launch a fait accompli out of a belief that a defender will accept the aggression, i.e., that the defender will accept a small loss of territory rather than invoke a broader war. 34 In some sense, a fait accompli becomes what Schelling called a “salami tactic” if it enables the attacker to gain some territory without inducing a response by the defender. 35 We propose an additional motivation: An aggressor might be tempted to launch a fait accompli if it believes that achieving the fait accompli will strengthen its defensive position, thereby further discouraging outside intervention by shifting the balance of power. A successful fait accompli might improve the attacker’s defensive position by providing geographic advantages were it to, say, capture an island or a mountain range. This would permit the attacker to construct stronger defensive positions or use the economic resources of the captured territory to boost its military power. 36 Strengthening the defensive position through any of these means raises the defender’s perceived cost of intervening, thereby dissuading it from taking action. Because democracies are very unwilling to intervene in wars with low chances of victory, 37 they might become discouraged and accept the conquest, albeit begrudgingly, if faced with the prospect of a long, difficult road to victory. Certainly, autocratic aggressors, such as Japan in 1941 and Argentina in 1982, hoped that their faits accomplis would discourage broader intervention from democratic defenders. Of course, the ability of a fait accompli to shift the military balance varies. The Soviet capture of West Berlin, for example, might not have provided communist forces either local geographical advantages or yielded economic resources that could have been converted to communist military power.

In short, there are good reasons to doubt that tripwire forces significantly boost deterrence. That said, believers in a tripwire effect inevitably point to the most well-known, apparently successful example of tripwire deterrence: the deployment of American and other NATO troops to West Berlin during the Cold War. During the Cold War, Western powers deployed as many as 12,000 troops in the city. This was not nearly enough to defend a city of 900,000, and yet peace obtained. Schelling and others inferred that, because the deaths of those troops in combat would have invoked immediate American intervention, the Soviets decided not to attack.

In the decades since Schelling wrote Arms and Influence , archives have been opened that cast doubt on his interpretation. They indicated that Stalin did not intend to invade West Berlin in 1948, nor did Khrushchev in the 1950s or early 1960s, meaning that tripwire forces did not deter an attack because there was no planned attack to deter. 38 Internal discussions within the East German and Soviet governments revolved around sustaining the East German economy and state, stemming the flow of migrants to the West, persuading the West to recognize East Germany, and the possibility of closing access to West Berlin. An actual invasion, including a fait accompli effort against West Berlin, was not discussed, even as a contingency. Further, his public threats and blusterous rhetoric notwithstanding, Khrushchev preferred to avoid actual confrontation with the West over Berlin. In June 1959, Khrushchev remarked privately, “[We] don’t think it’s worth it now to push the west to the wall, so that we will not give the impression that we are seeking the recognition of the GDR [German Democratic Republic]. The Americans don’t want to recognize the GDR.” 39

By 1961, as the refugee flow created an accelerating internal crisis for the East German government, there was not even passing mention of invading West Berlin as a solution. Rather, the more belligerent option — which was eventually chosen — was to close the border between East and West Germany. Internal Warsaw Pact discussions of military matters in the summer of 1961 surrounding this decision focused on what the Western reaction would be. The debate was over whether communist forces could deter NATO, not over whether they would invade West Berlin in light of American tripwire forces. 40

Flawed assumptions about tripwire deterrence underlie current NATO defense planning. Consider NATO’s strategy toward the Baltic states. 41 It presently deploys a battalion in each of the three Baltic states, each of which is “backstopped” by additional forces from Germany, the Czech Republic, and Norway, along with a brigade-sized U.S. force, which is stationed in Poland. 42 Some view these forces not as directed toward stopping a Russian invasion of a Baltic NATO member, but instead as a tripwire to provoke American involvement. 43 Michael O’Hanlon and Christopher Skaluba recently pointed out that these forces, dubbed NATO’s “enhanced forward deployment,” have not been “a truly integrated combat force; nor has [NATO] deployed many helicopters and air defense systems.” 44 An Atlantic Council report described NATO’s current strategy as relying on a “tripwire” and “rapid reinforcement,” warning that this approach does not adequately address Russia’s “time, space, and mass advantages,” affording Russia the ability to achieve a successful fait accompli . 45 In other words, NATO’s forward-deployed forces are simply not adequate in size, appropriately placed, or properly equipped to counter a Russian invasion. A 2016 RAND Corporation war game found that Russian forces could reach the outskirts of Riga and Tallinn in approximately 60 hours. 46 Given the rapidity of the NATO force’s defeat in the war game, the ability of Russian forces to achieve a fait accompli would leave NATO decision-makers with few feasible options. Would they be willing to initiate an all-out ground war, with the possibility of nuclear escalation? One must therefore seriously question the ability of these forces to “trip the alarm” for a sizeable counter-strike by NATO and the United States.

Deployments Beyond Tripwires

Tripwire-force deployments are insufficient to bolster deterrence because deterrence is about more than signaling. One must instead deploy a force that is sufficiently capable — one that can itself fulfill a deterrent threat. Troop deployments must be able to shift the local balance of power so as to alter the potential attacker’s likelihood of succeeding, or its likelihood of succeeding quickly and/or at a low cost. 47

There are three related ways in which forward-deployed troops can help fulfill a deterrent threat. First, they can give local forces a better chance of defeating the attacker’s forces through some combination of increasing troop quantity, improving military technology, and crafting an appropriate military strategy. 48 Even if the deployed forces were relatively small in number (but still larger than a simple tripwire force), they could be equipped with force-multiplying weaponry, such as advanced armor. 49 Foreign-deployed troops can also shift the local balance of power if equipped with the optimal military strategy. This was John Mearsheimer’s central policy conclusion in his classic 1983 book, Conventional Deterrence : that pre-deployed American troops armed with the right military strategy, and perhaps the right technology, could deter the Soviets from invading West Germany. 50 One element of military strategy is integrating with coalition partners. Alliance structures that plan for the effective, combined use of allied forces can serve as an especially powerful deterrent. 51 A sufficiently sized troop deployment could also defeat aggression from non-state actors. 52 Certainly, the number of deployed troops needed to shift the balance of power varies by context. Under some circumstances, a smaller contingent of troops could be adequate if troops in the region could be rapidly deployed before an aggressor could achieve a fait accompli . Offshore naval power could also play a role, permitting a smaller deployed force to accomplish its deterrence mission.

Tripwire-force deployments are insufficient to bolster deterrence because deterrence is about more than signaling. One must instead deploy a force that is sufficiently capable — one that can itself fulfill a deterrent threat. 

Second, even if deployed troops cannot fully blunt an attack, they can slow the attacking forces down. The prospect of a slowed advance can boost deterrence because attackers often seek rapid victory. Slowing an advance can buy time for the defender to deploy larger numbers of troops to the allied territory before it is conquered. If an attacker can be convinced that quick victory is unlikely, deterrence is more likely to hold. 53 Deployed troops that are focused on buying time can play a key role in enhancing the fighting capacity of the allies if they are substantial enough to allow the allies to execute a war plan, including permitting the timely mobilization of reinforcements to aid embattled, pre-deployed forces. A small tripwire force is also unlikely to buy much time, something that is not commonly the purpose of such a deployment. Again, the purpose of a tripwire force is to, in the words of Schelling, “die heroically,” not hold the line until help arrives.

Third, deployed troops can preserve peace by making attempts at faits accomplis less attractive. As discussed, the lure of a fait accompli is that if an attacker can rapidly conquer a territorial objective without engaging in military combat, it may be able to establish a strong defensive position, which would dissuade a counterattack or broader intervention. A substantial forward troop deployment can undermine a fait accompli strategy by reducing the likelihood that the attacker will capture the desired territory and strengthen its defensive position before a response can occur.

In summary, substantial deployments that shift the local balance of power are significantly more likely to deter aggression than tripwire forces are. Some might propose that more substantial troop deployments could boost credibility as well as capability, because such deployments might constitute a sunk cost signal of the defender’s willingness to intervene. It is possible that larger troop deployments convey such a sunk cost signal, though we do not yet have historical, quantitative, or survey research to demonstrate such an effect. Regardless, a key, underappreciated cause of deterrence failure is not an aggressor’s assessment of credibility, but rather its assessment of capability. As we demonstrate in our case studies below, aggressors attempt faits accomplis because they believe they can overwhelm defending forces and capture their territorial objective rapidly, emphasizing the importance capability plays in helping deterrence work.

That said, there are three limits to our argument that large contingents of deployed troops bolster deterrence through improving the capability of the allied state. First, an attacker that is less focused on winning quickly might not be deterred by an increased likelihood of delay. Non-democracies, for example, might be less motivated to win quickly as compared with democracies, because non-democratic leaders are less fearful of the domestic political consequences of a lengthy war. 54 North Vietnam was not deterred by the presence of U.S. troops in South Vietnam, in part, because it was willing to wage a long and costly war. 55 It is also conceivable that the defender might not have the motivation or ability to make use of a delay to provide more support to the ally. In short, the importance of delay may vary by context.

Second, deployed troops only help if they shift the attacker’s calculus of victory. That is, the mere presence of such troops is not sufficient. The troops need to be the right size, have the appropriate armament, be deployed to the right location, and have the right strategy to change the attacker’s calculations. 56 Consider the German attack on the West in 1940, and Belgium in particular. British troops were not deployed to Belgium in peacetime. If they had been, they likely would not have been sent to the area where Germany actually attacked — the Ardennes — because Allied intelligence did not expect the main German attack to take place there, and hence British peacetime deployments might not have deterred a German attack. 57

Third, if the ally is sufficiently well armed, then the peacetime deployment of the defender’s troops would not be necessary to strengthen an already robust deterrent. For example, Taiwan currently has sufficient conventional forces to repel a Chinese amphibious invasion, meaning that American force deployments there would likely add little to an already strong capability. 58 Similarly, the Israeli Defense Forces are currently sufficiently strong to defeat any conventional ground attack from neighboring countries, making the peacetime deployment of American troops there unnecessary from a capabilities perspective. One policy implication of this is that a defender may be able to maintain a robust deterrent for an ally, not by deploying forces, but by offering substantial material aid to the ally, as the United States does for Taiwan and Israel.

History Rewritten? Three Critical Cases of Forward Troop Deployments

We test our theory that tripwire troop deployments will not significantly bolster deterrence, but that more substantial troop deployments will, by examining how troop deployments affected three attempts at deterrence in the 20th century: America’s attempt in 1949 to deter a North Korean attack on South Korea; America’s attempt in 1950 to deter a North Korean attack on South Korea; and Britain’s actions (and largely inactions) to deter a German attack on Belgium in 1914. First, North Korea did not attack South Korea in 1949, in part, because an adequately sized American troop deployment to South Korea shifted the local balance of power. Second, North Korea did attack South Korea in 1950, in part, because American troop deployments to South Korea had been reduced to a tripwire force that was insufficient to shift the local balance of power. Third, British troop deployments to Belgium in 1914 could have deterred a German attack if they had been sufficient to shift the local balance of power. However, a small tripwire force that did not shift the local balance of power would likely not have been sufficient to deter Germany. We chose these cases because they offer variation in the number of troops the defending power deployed (i.e., our independent variable), there are primary documents that provide insight into key decisions made in these cases, and the cases themselves are highly significant in world history and U.S. foreign policy.

Korea, 1949 & 1950

After World War II, the former Japanese colony of Korea was divided into two independent countries: communist North Korea and non-communist South Korea. The leaders of both countries, Kim Il Sung of North Korea and Syngman Rhee of South Korea, envisioned invading the other Korea and unifying the peninsula under a single government. Kim knew he required Soviet assistance and support to carry out a successful campaign. South Korea became a member of the United Nations in December 1948, placing it under the purview of the U.N. Charter’s Chapter 1 commitment to remove threats and suppress acts of aggression.

In March 1949, Kim first contacted Soviet leader Joseph Stalin about possible Soviet support for an invasion. Stalin “did not object in principle” to Kim’s plan to attack South Korea. 59 However, Stalin declined to approve and support such an attack. 60 He reached this decision after an extended discussion with Kim about the local balance of power on the Korean Peninsula. The presence of the American forces stationed in South Korea — first deployed there in September 1945 — was of great importance to Stalin. When Kim asked permission to invade the South, Stalin’s first question was to ask how many American troops were stationed there. Kim informed Stalin that as many as 20,000 American forces were there, a very sizable contingent given that the entire South Korean army at that point numbered only 60,000, in Kim’s estimation. 61 Stalin expressed concern with the local balance of forces and identified the American troop deployments in the South as one of the key reasons why he was declining to support a North Korean attack, recognizing that American troops would “interfere in case of hostilities.” 62 In 1949, then, deterrence held on the Korean Peninsula.

Although Stalin declined to support a North Korean attack on the South in March 1949, Moscow continued to monitor the American troop presence in South Korea. In a secret May 1949 report to Moscow, Soviet intelligence reported that the American and South Korean governments were in the process of negotiating reductions in the American troop presence. 63 In September 1949, Moscow asked Pyongyang directly if there were still American troops in South Korea, and how much assistance those troops could offer in the event of a North Korean invasion. North Korea estimated there were between 500 and 2,400 U.S. troops left in South Korea and that, in the event of war, “American instructors will take immediate part in organizing military actions.” 64 Internally, American leaders recognized that this reduction in troops would change the U.S. troop presence in South Korea to a “trip-wire.” 65

In early 1950, Kim again pressed Stalin to support an invasion. He understood that Stalin demanded rapid victory. In a visit to Moscow in early January, Kim stressed that his army could capture the South Korean capital of Seoul, located near the border, in a matter of days. 66 Stalin began to relax his opposition in late January, though he maintained that an invasion must be planned such that “there would not be too great a risk.” 67 Stalin saw political advantages to a Korean war: It would help Moscow maintain control of the communist world and prevent China from becoming a challenger for communist leadership.

Kim returned to Moscow in April, and, over the course of this visit, Stalin gave his approval for an invasion. Kim reiterated that the campaign would be over within days and Stalin was persuaded. 68 He understood that now a North Korean fait accompli was possible, offering victory before America could send substantial reinforcements. As Stalin declared to Kim that month, “The war should be quick and speedy. Southerners and Americans should not have time to come to their senses. They won’t have time to put up a strong resistance and to mobilize international support.” 69 Note Stalin’s mention of “strong” resistance, recognizing that North Korea would confront the weak American tripwire forces — a few hundred troops — that were then deployed to South Korea.

Stalin expressed concern with the local balance of forces and identified the American troop deployments in the South as one of the key reasons why he was declining to support a North Korean attack, recognizing that American troops would “interfere in case of hostilities.”

Kim sought to reassure Stalin that his plan for a fait accompli would avoid the risk of broader American intervention. Kim said that, once the attack had begun, there would be a mass uprising within South Korea against the Rhee government in support of the communist liberation: “Americans won’t have time to prepare and by the time they come to their senses, all the Korean people will be enthusiastically supporting the new government.” 70 That is, the fait accompli would help shift the local balance of power against the United States because, after a North Korean victory, the South Korean population would rally to accept and support communist rule.

After Stalin approved the attack in April 1950, he remained focused on the urgency of North Korea achieving a rapid fait accompli . The June 15, 1950 operational plan called for an initial attack on the Ongjin Peninsula on the west coast of South Korea, just over the 38th parallel border. 71 This would be followed by the capture of the capital of Seoul, also near the border, and the destruction of the South Korean military. Last, other major cities would be captured and the entirety of the country would be liberated. Stalin continued to stress the need for utmost secrecy, perhaps fearing that, if America sensed an impending invasion, it might send more troops to South Korea. Initial reports of U.S. casualties after the June 25 invasion, specifically of American bombers being shot down, did not disrupt Stalin’s plan of pressing for rapid victory to avoid broader American involvement. Upon hearing these reports, Stalin directed the Soviet ambassador to North Korea to convey to Kim that “the sooner South Korea is liberated the less chance there is for [American] intervention.” 72

In summary, it appears Stalin became willing to approve the North Korean invasion of South Korea when he was confident the North could achieve a fait accompli . The substantial reduction of U.S. forces in South Korea, from a consequential detachment to a tripwire force, helped provide this confidence. The evidence does not indicate that the reduction in U.S. forces in South Korea was necessary and sufficient to cause a North Korean invasion, but it does indicate that the communists desired a rapid fait accompli victory; that they realized that the size of the U.S. troop deployments to South Korea affected the likelihood of that victory; and that, as of fall 1949, those troops had been reduced.

One alternative perspective is that the key factor pushing Stalin to greenlight the invasion was not the shifting local balance of power caused by a reduction in U.S. troops, but rather Stalin’s conclusion by January 1950 that America was unwilling to intervene, i.e., that Stalin had doubts about America’s credibility, rather than America’s capability. This view posits that Stalin may have been especially encouraged by Secretary of State Dean Acheson’s January 1950 speech that appeared to place South Korea outside of the American defense perimeter, as Acheson declared that the perimeter “runs along the Aleutians to Japan and then goes to the Ryukyus.” 73

Two comments are in order. First, the effects of the 1950 Acheson speech on communist decision-making ought not be exaggerated. Other parts of the speech cast doubt on the idea that America would stand aside in the event of an invasion of South Korea, as Acheson specifically indicated that the United Nations would resist aggression anywhere in the Pacific region. Indeed, the media coverage of the speech implied that South Korea was inside the U.S. defense perimeter. 74 Importantly, as noted, in the first half of 1950, after Acheson’s speech, Stalin continued to express concern about the possibility of broader American intervention, emphasizing the need for secrecy and the importance of rapid victory in the South. This was not so much a dismissal of America as an irrelevant paper tiger but rather indicates the importance of accomplishing a rapid fait accompli before broader intervention could occur. As one team of historians summarized it, by May 1950,

Stalin would have concluded from press reports and intelligence that, though the Americans might want to aid … South Korea, it would take many months to mass and get that aid to the western Pacific. The timing was on Kim’s side if he moved quickly and decisively. 75

Second, new documentary evidence reveals that, in internal discussions, Soviet and Chinese officials did not take Acheson’s speech as a genuine statement of American disinterest in defending South Korea. Rather, they described Acheson’s speech as “slander,” an attempt to “deceive directly public opinion,” and a “smokescreen.” 76 Based on the recent revelation of this and other internal documents, historian Kim Donggil has concluded, “The argument that Acheson’s speech about South Korea resting outside the U.S. defensive perimeter was the deciding factor in Stalin’s decision does not accord with the facts.” 77 Another historian concurred, arguing that “recently released Soviet documents [demonstrate] that Acheson’s address had little if any impact on Communist deliberations.” 78

World War I

In 1914, the German war strategy depended on rapidly conquering Paris. Germany’s two major adversaries in 1914 were France and Russia, which were allied with each other. Germany recognized that war against one would mean war against both, and war against two major powers simultaneously would be a risky endeavor. Germany’s solution to this problem was the Schlieffen Plan, initially devised in 1905 by then-Chief of the German General Staff Marshal Alfred von Schlieffen. 79 Russia’s underdeveloped railroad network meant that the mobilization of its military would take weeks. If Germany could conquer France quickly, German forces could then rapidly redeploy to the east to confront the Russian colossus just as it was becoming ready for war. Moreover, the rapid German conquest of France and Belgium would dissuade Britain from entering a war against Germany. And control of the French coasts would facilitate the use of German submarines and air power against Britain. French and Belgian financial resources could be used to bolster German naval power, eventually permitting a successful German naval blockade of Britain, and thereby compelling Britain to accept German continental hegemony. 80 This is the military attraction of the fait accompli . Once achieved, it shifts the balance of power in the attacker’s favor, dissuading the defender from continuing the war.

Critically, the rapid conquest of France required the invasion of neutral Belgium, as the Franco-German frontier was relatively mountainous, making any attack there unattractive. 81 The importance of conquering Belgium and France rapidly cannot be overstated. Kaiser Wilhelm recognized this at least as early as 1905. 82 When Britain seemed, in early August 1914, to suggest it would remain neutral if Germany did not attack Belgium, Germany rejected the possibility because staying out of Belgium would fatally slow the pace of its offensive. Chief of the German General Staff Helmuth von Moltke commented on August 4,

An attack from German territory [directly to France] would have cost the German army 3 months and would have ensured Russia such a head start that we could no longer have reckoned on a success on both fronts. We had to go via Belgium with all our might on Paris for a quick reckoning with France. This was the only way to victory. 83

Britain did not pre-deploy any troops, not even tripwire forces, to Belgian territory in 1914. If it had pre-deployed troops in sufficient numbers to shift the local balance of power, a possibility made politically difficult by Belgium’s official neutrality, 84 Germany would have been deterred and World War I might well have been avoided. German forces would have had to face British forces from the outset of hostilities, as opposed to several days or weeks after the war’s outbreak. Schlieffen assumed that, absent the pre-deployment of troops, British forces would not be able to land soon after the outbreak of war:

If in a Franco-German war the English plan to land a force of 100,000 men or more in Antwerp, they can hardly do so in the first days of mobilization. No matter how well they prepare the assembly of their three army corps, their army organization and defence system present so many difficulties that their sudden appearance within the great Belgian fortress is almost inconceivable. 85

Moltke agreed. 86 Schlieffen was confident that British forces landing after the start of hostilities would not slow down the German push through Belgium into France. 87 Schlieffen also scoffed at the prospect of a blockade by the Royal Navy, confident that a short ground war would end the conflict. 88

Schlieffen recognized that the prewar deployment of British troops to Belgium would spoil the chances of a rapid conquest, imperiling the entire plan. He wrote in 1912,

A successful march through Belgium on both sides of the Meuse is therefore the prerequisite of a victory. It will succeed beyond doubt, if it is only the Belgian army which tries to obstruct it. But it will be very difficult if the English army, and perhaps even part of the French, is present. 89

Maj. Gen. Wilhelm von Hahnke commented in 1911, “Belgian neutrality must be broken by one side or the other. Whoever gets there first, occupies Brussels and imposes a war-levy of some thousand millions, has the upper hand.” 90 Moltke was of the same opinion: “The enterprise is only possible if the attack is made at once, before the areas between the forts are fortified.” 91 The German military and political leadership, including the Kaiser, Chancellor Theobald von Bethmann-Hollweg, Adm. Alfred von Tirpitz, and Moltke, all agreed with Schlieffen that the key questions were not only whether Britain would intervene, but also when British troops might arrive. 92

The focus on seizing Belgium quickly did not shift when Moltke succeeded Schlieffen in planning Germany’s military strategy. However, Moltke did alter another area of Germany’s strategy, which heightened the need for quick success. Moltke decided to respect Dutch neutrality, making it crucial to seize the Belgian fortress city of Liège at the very outset of the conflict, a task much more easily accomplished if a substantial peacetime garrison were not present. 93 In the words of one historian, “the quick seizure of Liège … was … regarded as an indispensable precondition for the successful execution of the great wheeling movement into northeastern France.” 94 The city of Liège was surrounded by a system of 12 forts, meaning the German advance would have to take these forts quickly to succeed.

The Belgian military was, by itself, unable to defend the Liège fortresses, both because of insufficient numbers (Belgian troops were dispersed throughout the country) and because Belgian troops themselves were inadequately trained and equipped. 95 The Belgian chief of staff in 1913 estimated that 60,000 troops would be needed to defend Liège, but, when German troops attacked in August 1914, there were only 25,000 Belgian defenders present. 96 The Germans contemptuously dismissed Belgian troops as “chocolate soldiers.” 97 Moltke declared, “We can count on the somewhat inefficient Belgian forces being quickly scattered.” 98 As war broke out and German forces advanced on Liège, the Belgian leadership hoped for the rapid arrival of Anglo-French forces to bolster its defenses there. 99 French forces were not sent, and British forces arrived too late to help. Defended only by Belgian troops, Liège fell to Germany on August 17, only two days later than the German war plan had envisioned. 100

British defense planners recognized that the Belgians by themselves might not be able to hold on to the Meuse forts, including at Liège, and that, if the forts fell to Germany, British troops could not arrive in time to help save Belgium.

Strikingly, British military planners agreed with Schlieffen. As early as 1906, they recognized that Germany would gain military advantage by going through Belgium to invade France and that the speed of substantial British troop deployments would be essential to thwarting German plans. The British regretted that the projected transport schedule of British troops would not allow for those troops to arrive in time. British officers understood that “Time is of the greatest importance.” 101 They understood that the Germans were focused on making “ every possible effort to press on and to try to beat us” in reaching Belgian territory. 102 Significantly reducing the time by which British troops could arrive in Belgium to confront the German invaders would provide “immense gain.” 103 British defense planners recognized that the Belgians by themselves might not be able to hold on to the Meuse forts, including at Liège, and that, if the forts fell to Germany, British troops could not arrive in time to help save Belgium. 104 A high-level 1911 British report reiterated that Germany might launch a surprise attack on Liège and that Belgian troops would be inadequate to defend it alone. 105 The British also recognized the low quality of the Belgian troops. 106 As late as May 1914, the British military noted that the critical Belgian fortresses, “if defended only by its peacetime [Belgian] garrison, would fall an easy prey to a German coup de main , executed at the outset of hostilities.” 107

One piece of evidence that substantial peacetime British troop deployments — meaning larger than a token tripwire force — could have shifted the local balance of power decisively enough to alter German plans in summer 1914 was discussion among German military planners of expected increases in Belgian forces. Belgium began to consider improving its military following the 1911 Agadir military standoff between French and German forces and, in 1913, passed a bill calling for the substantial expansion of the army, from 180,000 to 250,000 troops. While German military planners understood that an improvement in Belgian defenses would undermine the viability of the Schlieffen Plan, they reassured themselves that implementation would be slow. Indeed, though Russia’s growing power over time has traditionally been seen as an incentive for Germany to launch a preventive war, growth in Belgian power over time created similar incentives. This was not because Belgium threatened Germany, but because additional Belgian forces render impossible the quick advances the Schlieffen Plan required. 108 Germany’s focus on Belgian military power supports the claim that substantial British troop deployments would have eliminated Germany’s incentives to launch a preventive war in the West, because the local balance of power would have been immediately shifted against Germany, rather than more slowly through the process of Belgian military reforms.

In short, the weakness of Belgian forces, coupled with the absence of adequate British forces in the summer of 1914, fatally weakened prospects for deterring Germany from attacking Belgium. Even if British troop deployments had not been large enough to completely stop the German advance, as long as they were sufficient to slow down German troops this would have disrupted the tight schedule necessary for implementing the Schlieffen Plan. Germany’s decision to allow Austria to attack Serbia was predicated on the assumption that, if the conflict escalated, Britain would not disrupt the rapid conquest of Belgium. If Germany had not been confident in British military irrelevance, it would have restrained Austria, avoiding a broader war. 109

A counterargument to our claim is that a small British tripwire force, rather than a large contingent, could have deterred Germany, given that German war plans required Britain remaining neutral. If British troops deployed in Belgium were killed in the first days of the war, British intervention would have been inevitable, even if those troops had not been able to slow or stop the German march through Belgium. But we maintain, based on the views of the German military with regard to British neutrality, that deployment of a smaller tripwire British contingent insufficient to shift the local balance of power would not have deterred Germany.

To understand how German officials viewed British neutrality, one should focus on the views of German military leaders rather than German civilian leaders. 110 German military leaders were not concerned about Britain maintaining neutrality. The German military recognized that the operational necessity of invading Belgium made eventual British intervention inevitable. Moreover, the German military leaders would not have been deterred even if they fully believed that Britain was going to intervene, as long as that intervention was not immediate. 111 Indeed, in prewar planning discussions, German military leadership appeared unconcerned with Britain remaining neutral. They assumed that British ground forces would eventually arrive, but too late to prevent the German conquest of Belgium and France. 112 Historian Annika Mombauer put it starkly, “That Britain would not remain neutral was a mere hiccough for the [German] General Staff.” 113 Some German generals even welcomed British intervention, craving the opportunity to defeat British forces in battle, likely assuming that British intervention would be too little, too late to save Belgium or France. 114

Moltke’s invasion plan of Belgium actually presumed the eventual presence of British troops on Belgian soil. 115 More broadly, he assumed that British intervention in a European war would be inevitable “because England considers Germany stronger than France, is afraid of German hegemony and wants to preserve the balance in Europe.” 116 To this end, Moltke wanted to respect Dutch neutrality, in order to protect the German flank in anticipation of British intervention following a German invasion of Belgium. 117 On August 4, Moltke declared that seizing Belgium was sufficiently important that it must be done, even if this meant British intervention. 118 Moltke also argued that Germany ought to ignore any British commitment to stand aside if Germany respected Belgian neutrality, because such a commitment would not be credible given the threat to the European balance of power if Germany defeated France. 119

Thus, British troop deployments before July 1914 (or earlier) would have been unlikely to persuade the German military to avoid war if their only function was to increase the likelihood of British intervention. However, pre-deployed British forces might have persuaded the German military to avert war, by shifting the local balance of forces against Germany and slowing the German advance. In short, the peacetime dispatch to Belgium of a moderate British troop contingent might have prevented what became, at the time, the deadliest war in the history of humanity.

Implications for U.S. Foreign Policy

As a policy tool, forward troop deployments are misunderstood in two ways. First, small tripwire deployments do not necessarily have powerful credibility effects, as is often thought. That is because it is not certain that the prospect of a small number of American troop fatalities would automatically engender broader American military intervention. Second, the capability effects of larger troop deployments are underappreciated. If forward troop deployments can substantially shift the local balance of power, even if only by slowing down an attacker’s advance, they can complicate an attacker’s plans and reduce the likelihood of aggression.

The limited utility of tripwire troop deployments should push decision-makers to reject tripwire deployments and instead consider two other options. First, if decision-makers are unwilling to bear the costs of more substantial troop deployments in order to deter attacks on allies, then they should consider reducing foreign commitments to conserve resources. Indeed, advocates of strategic restraint have directly suggested that the United States should eschew tripwire deployments as costly and ineffective. 120

Second, if decision-makers are motivated to deter aggression abroad, they should recognize that successful deterrence requires more substantial foreign troop deployments.

This would have important implications for a variety of potential global hotspots. Consider the Russian threat to the Baltic states and Poland, all NATO members. The general concern among NATO commanders is that Russia could overrun tripwire forces and accomplish a quick fait accompli land grab. It could then consolidate its seizure through propaganda, a ceasefire agreement recognizing its territorial capture, and a veiled nuclear threat to deter a NATO counterattack. 121 More substantial troop deployments to shift the local balance of power would reduce this risk. At the 2016 Warsaw Summit, NATO agreed to expand its troop commitment to these states, building four multilateral battle groups, each of which contains about 1,200 troops. However, as noted above, some viewed these contingents as inadequate to shift the balance of power, arguing that their aim was to achieve “deterrence by trip wire.” 122 Even with these troop commitments, Russia might be tempted to launch a fait accompli , capturing territory before NATO could amass a more sizable force. 123 There is also concern about a possible Russian fait accompli attack against the Norwegian Arctic island of Svalbard. Deploying a substantial numbers of troops there, rather than a small tripwire force, could discourage such an attack. 124

[I]f decision-makers are unwilling to bear the costs of more substantial troop deployments in order to deter attacks on allies, then they should consider reducing foreign commitments to conserve resources.

Deploying a more significant number of troops could also help deter Chinese aggression. Andrew Krepinevich has proposed an integrated defense of the Japanese-Filipino-Taiwanese archipelago, a plan that includes the pre-deployment of U.S. troops to the region to alter Chinese military calculations of the local balance of power. 125 Specifically, pre-deployment and peacetime training exercises involving Japan and the United States on the Senkaku/Diaoyou Islands in the East China Sea could discourage China from launching a fait accompli attack there. 126

Our argument also sheds light on U.S. troop deployments to South Korea. A key question is whether current troop deployments to South Korea — about 28,000 troops — really change the local balance of power. Some have argued that the only significant contribution to deterrence the current American troop deployment can make is through tripwire effects, making a broader intervention more likely. 127 Our argument suggests that U.S. troops deployed to South Korea will boost deterrence but only if they appreciably change the local balance of power. If such a force is deemed by defense planners to be insufficiently sized or structured to change the balance of power, then increasing or altering U.S. forces deployed to South Korea would provide deterrence benefits. 128

Our argument also applies to U.S.-Japanese defense planning. Some propose that the deployment of American troops to Japanese territory, such as Okinawa, can deter an attack through a tripwire effect. 129 However, the mere presence of such troops does not necessarily deter an attacker. Deployments must be adequate to shift the local balance of power.

Last, our argument is germane to debates about peacekeeping. Some advocates of peacekeeping have made tripwire arguments that the presence of peacekeepers deters former insurgents from breaking the peace because the deaths of any peacekeeping troops in combat would ensure more substantial international intervention. 130 However, the early 1990s demonstrated that peacekeepers did not generate this credibility effect: Overpowered peacekeepers were captured in Bosnia and others were massacred in Rwanda, waiting in vain for rescue reinforcements that did not arrive. Peacekeepers act as a deterrent if they can shift the attacker’s calculus. This may require deployment in sufficient numbers or with the right equipment, such as armor.

We recognize that the pre-deployment of troops capable of shifting the local balance of power has clear limitations. Beyond the need to tailor any deployment to the local combat environment, increased troop deployments may raise financial costs that the public is unwilling to bear. Public opinion polls indicate Americans are hesitant about the prospect of raising defense spending. 131 In a fiscal environment in which the COVID-19 pandemic has placed pressure on, and prompted a reconsideration of, the U.S. defense budget, 132 increasing resources for foreign troop deployments may not be feasible. Moreover, increased troop deployments could create a moral hazard problem. Specifically, an ally that perceives greater protection from the United States could, in turn, feel more at liberty to engage in provocative or even aggressive action, knowing that it can rely on America for protection if the situation escalates. Some have proposed that moral hazard risks can be reduced by including language in alliance treaties that requires American intervention only if the ally was attacked first. However, others have observed that such “defensive wars” language can be vague, meaning that, even if an ally engages in provocative action, it can still argue that it was attacked first, triggering the alliance commitment. 133

The general policy implications of our paper are that policymakers should beware of assuming that small troop deployments can have outsized deterrence effects, and they should recognize that larger and more considered deployments may be necessary to provide real deterrence. Toward the end of the Obama administration, observers argued for just this: the need to move past Cold War faith in tripwire effects and instead devote more resources to the Army to boost troop deployments abroad: “Put simply, forward deployed soldiers and marines are more than just trip-wires and hostages. Allies do not have faith in American commitments because American troops might die; they have faith because American troops can kill and win.” 134

Dr. Dan Reiter is Samuel Candler Dobbs Professor of Political Science at Emory University. He is the award-winning author or co-author of dozens of articles and several books, including How Wars End (Princeton, 2009) and Democracies at War (Princeton, 2002, with Allan C. Stam).

Dr. Paul Poast is associate professor of political science at the University of Chicago and a non-resident fellow of the Chicago Council on Global Affairs. He is the author or co-author of three books, Economics of War (McGraw Hill-Irwin, 2006), Organizing Democracy (University of Chicago Press, 2018, with Johannes Urpelainen), and Arguing About Alliances (Cornell University Press, 2019).

Acknowledgements : An earlier version of this paper was presented at the 2019 annual meeting of the American Political Science Association meeting. We thank the participants of that panel for comments, especially those of Etel Solingen, Jack Levy, and Hein Goemans. For research assistance, thanks to Stefano Jud.

Image: U.S. Marine Corps photo by Lance Cpl. Kaleb Martin

1 Mark David Neiman, et al., "An International Game of Risk: Troop Placement and Major Power Competition," Journal of Politics (forthcoming), https://doi.org/10.1086/711716 .

2 Robert Jervis, The Logic of Images in International Relations (Princeton, NJ: Princeton University Press, 1970). Some recent scholarship is more confident that verbal statements in international relations are credible, or at least can be credible. See Anne E. Sartori, Deterrence by Diplomacy (Princeton, NJ: Princeton University Press, 2005); John J. Mearsheimer, Why Leaders Lie: The Truth About Lying in International Politics (Oxford: Oxford University Press, 2011); and Robert F. Trager, Diplomacy: Communication and the Origins of International Order (Cambridge: Cambridge University Press, 2017).

3 David Choi, “Trump Reportedly Asked the Pentagon to Explore Withdrawing U.S. Troops from Germany,” Task & Purpose , June 30, 2018, https://taskandpurpose.com/trump-pentagon-withdraw-troops-germany/ ; and Mark Landler, “Trump Orders Pentagon to Consider Reducing U.S. Forces in South Korea,” New York Times , May 3, 2018, https://www.nytimes.com/2018/05/03/world/asia/trump-troops-south-korea.html .

4 Brad Howard, “Marines May Be Headed for Taiwan for the First Time Since 1979,” Task & Purpose , June 29, 2018, https://taskandpurpose.com/marines-taiwan-china-mattis .

5 Karl Friedhoff, “US Troop Drawdown in South Korea Worth Considering,” The Hill , February 29, 2019, https://thehill.com/opinion/national-security/430428-us-troop-drawdown-in-south-korea-worth-considering .

6 Robert Jervis, Perception and Misperception in International Politics (Princeton, NJ: Princeton University Press, 1976), chap. 2.

7 Joshua C. Fjelstul and Dan Reiter, “Explaining Incompleteness and Conditionality in Alliance Agreements,” International Interactions 45, no. 6 (2019): 946–1002, http://doi.org/10.1080/03050629.2019.1647838 .

8 Thomas C. Schelling, Arms and Influence (New Haven, CT: Yale University Press, 1966), 22. See also Alexander L. George and Richard Smoke, Deterrence in American Foreign Policy: Theory and Practice (New York: Columbia University Press, 1974), 393.

9 Glenn Snyder similarly conflated these motives: “Some trip-wire effect could be realized with only token forces from the extra-Continental countries; an attack on such forces would implicate the honor, prestige, and other emotional values of these countries.” Glenn H. Snyder, Deterrence and Defense: Toward a Theory of National Security (Princeton, NJ: Princeton University Press, 1961), 130–31.

10 This work is indeed extensive. As a sample, see John J. Mearsheimer, "Nuclear Weapons and Deterrence in Europe," International Security 9, no. 3 (Winter 1984/1985): 19–46, https://www.jstor.org/stable/2538586?seq=1 ; Jacek Kugler, "Terror Without Deterrence: Reassessing the Role of Nuclear Weapons," Journal of Conflict Resolution 28, no. 3 (September 1984): 470–506, https://journals.sagepub.com/doi/10.1177/0022002784028003005 ; Daniel S. Geller, “Nuclear Weapons, Deterrence, and Crisis Escalation,” Journal of Conflict Resolution , 34, no. 2 (June 1990): 291–310, https://doi.org/10.1177/0022002790034002006 ; Kenneth N. Waltz, "Nuclear Myths and Political Realities," American Political Science Review 84, no. 3 (September 1990): 731–45, https://doi.org/10.2307/1962764 ; Robert Powell, Nuclear Deterrence Theory: The Search for Credibility (Cambridge: Cambridge University Press, 1990); Keir A. Lieber and Daryl G. Press, "The New Era of Nuclear Weapons, Deterrence, and Conflict," Strategic Studies Quarterly 7, no. 1 (Spring 2013): 3–14, https://www.jstor.org/stable/26270573?seq=1#metadata_info_tab_contents ; and Robert Jervis, Meaning of the Nuclear Revolution: Statecraft and the Prospect of Armageddon (Ithaca, NY: Cornell University Press, 1989).

11 For early work on the idea of tactical nuclear weapons, see Henry A. Kissinger, "Force and Diplomacy in the Nuclear Age," Foreign Affairs 34, no. 3 (April 1956): 349–66, https://www.jstor.org/stable/20031169?seq=1 ; and Morton H. Halperin, "Nuclear Weapons and Limited War," Journal of Conflict Resolution 5, no. 2 (June 1961): 146–66, https://journals.sagepub.com/doi/abs/10.1177/002200276100500203?journalCode=jcrb . For more recent discussion, see Matthew Fuhrmann and Todd S. Sechser, “Signaling Alliance Commitments: Hand-Tying and Sunk Costs in Extended Nuclear Deterrence,” American Journal of Political Science 58, no. 4 (October 2014): 919–35, https://doi.org/10.1111/ajps.12082 . For the use-it-or-lose-it logic applied to US nuclear forces on the Korean Peninsula, see Vipin Narang and Ankit Panda, “Command and Control in North Korea: What a Nuclear Launch Might Look Like,” War On the Rocks , Sept. 15, 2017, https://warontherocks.com/2017/09/command-and-control-in-north-korea-what-a-nuclear-launch-might-look-like .

12 Snyder, Deterrence and Defense , 133, note 13.

13 For an overview of the audience costs literature, see Bruce Bueno de Mesquita and Alastair Smith, "Domestic Explanations of International Relations," Annual Review of Political Science , no, 15 (2012): 161–81, https://doi.org/10.1146/annurev-polisci-070209-174835 ; and Allan Dafoe, Jonathan Renshon, and Paul Huth, "Reputation and Status as Motives for War," Annual Review of Political Science , no. 17 (2014): 371–93, https://doi.org/10.1146/annurev-polisci-071112-213421 . The audience costs literature fits in the broader literature on bargaining and war, as it is a proposed mechanism by which a threat of violence can eventually translate into the actual use of force. Moreover, it is a mechanism of “bargaining theory” that is susceptible to empirical evaluation. See Erik A. Gartzke and Paul Poast, "Empirically Assessing the Bargaining Theory of War: Potential and Challenges," in Oxford Research Encyclopedia of Politics (Oxford: Oxford University Press, 2017), https://doi.org/10.1093/acrefore/9780190228637.013.274 ; and Dan Reiter, “Exploring the Bargaining Model of War,” Perspectives on Politics 1, no. 1 (March 2003): 27–43, https://doi.org/10.1017/S1537592703000033 .

14 James D. Fearon, “Signaling Foreign Policy Interests: Tying Hands Versus Sinking Costs," Journal of Conflict Resolution 41, no. 1 (February 1997): 68–90, https://journals.sagepub.com/doi/10.1177/0022002797041001004 ; and Fuhrmann and Sechser, “Signaling Alliance Commitments.”

15 Fearon, “Signaling Foreign Policy Interests,” 69; and James D. Morrow, "Alliances, Credibility, and Peacetime Costs," Journal of Conflict Resolution 38, no. 2 (June 1994): 270–97, https://doi.org/10.1177/0022002794038002005 .

16 Scott D. Sagan and Benjamin A. Valentino, “Revisiting Hiroshima in Iran: What Americans Really Think About Using Nuclear Weapons and Killing Noncombatants,” International Security 42, no. 1 (Summer 2017): 41–79, muse.jhu.edu/article/667391 .

17 Robert E. Harkavy, "Defeat, National Humiliation, and the Revenge Motif in International Politics," International Politics 37, no. 3 (2000): 345–68, https://doi.org/10.1057/palgrave.ip.8890515 .

18 Peter Liberman, "An Eye for an Eye: Public Support for War Against Evildoers," International Organization 60, no. 3 (July 2006): 687–722, https://doi.org/10.1017/S002081830606022X ; and Rachel M. Stein, “War and Revenge: Explaining Conflict Initiation by Democracies,” American Political Science Review 109, no. 3 (August 2015): 556–73, https://doi.org/10.1017/S0003055415000301 .

19 The same can be said for leaders. Daryl Press holds that concerns about reputation do not matter to leaders in Calculating Credibility: How Leaders Assess Military Threats (Ithaca, NY: Cornell University Press, 2005). Others point to reputational concerns being conditional, not absolute. See Joshua D. Kertzer, Resolve in International Politics (Princeton, NJ: Princeton University Press, 2016); Danielle L. Lupton Reputation for Resolve: How Leaders Signal Determination in International Politics (Ithaca, NY: Cornell University Press, 2020); Keren Yarhi-Milo, Who Fights for Reputation: The Psychology of Leaders in International Conflict (Princeton, NJ: Princeton University Press, 2018); and Roseanne W. McManus Statements of Resolve: Achieving Coercive Credibility in International Conflict (Cambridge: Cambridge University Press, 2017).

20 Joshua D. Kertzer, and Ryan Brutger, "Decomposing Audience Costs: Bringing the Audience Back Into Audience Cost Theory," American Journal of Political Science 60, no. 1 (January 2016): 234–49, https://doi.org/10.1111/ajps.12201 . See also William G. Nomikos and Nicholas Sambanis, "What Is the Mechanism Underlying Audience Costs? Incompetence, Belligerence, and Inconsistency," Journal of Peace Research 56, no. 4 (July 2019): 575–88, https://doi.org/10.1177/0022343319839456 .

21 Jack Snyder and Erica D. Borghard, “The Costs of Empty Threats: A Penny, Not a Pound,” American Political Science Review 105, no. 3 (August 2011): 437–56, https://doi.org/10.1017/S000305541100027X ; and Marc Trachtenberg, “Audience Costs: An Historical Analysis,” Security Studies 21, no. 1 (2012): 3–42, https://doi.org/10.1080/09636412.2012.650590 .

22 Jack S. Levy, et al., “Backing Out or Backing In? Commitment and Consistency in Audience Cost Theory,” American Journal of Political Science 59, no. 4 (October 2015): 988–1001, https://doi.org/10.1111/ajps.12197 .

23 Stein, “War and Revenge”; Yarhi-Milo, Who Fights ; and Allan Dafoe and Devin Caughey, “Honor and War: Southern US Presidents and the Effects of Concern for Reputation,” World Politics 68, no. 2 (April 2016): 341–81, https://doi.org/10.1017/S0043887115000416 .

24 Matthew S. Levendusky and Michael C. Horowitz, "When Backing Down Is the Right Decision: Partisanship, New Information, and Audience Costs," Journal of Politics 74, no. 2 (April 2012): 323–38, https://doi.org/10.1017/S002238161100154X ; and Robert F. Trager and Lynn Vavreck, “The Political Costs of Crisis Bargaining: Presidential Rhetoric and the Role of Party,” American Journal of Political Science 55, no. 3 (July 2011): 526–45, https://doi.org/10.1111/j.1540-5907.2011.00521.x .

25 Stein, “War and Revenge,” 559.

26 Scott Sigmund Gartner and Gary M. Segura, Costly Calculations: A Theory of War, Casualties, and Politics (Cambridge: Cambridge University Press, 2021).

27 James Burk, “Public Support for Peacekeeping in Lebanon and Somalia: Assessing the Casualties Hypothesis,” Political Science Quarterly 114, no. 1 (Spring 1999): 53­–78, https://doi.org/10.2307/2657991 .

28 Dan Reiter, “Democracy, Deception, and Entry Into War,” Security Studies 21, no. 4 (2012): 611–12, https://doi.org/10.1080/09636412.2012.734229 .

29 Michael Tomz, "Domestic Audience Costs in International Relations: An Experimental Approach," International Organization 61, no. 4 (2007): 829, https://doi.org/10.1017/S0020818307070282 .

30 Graeme A. M. Davies and Robert Johns, “Audience Costs Among the British Public: The Impact of Escalation, Crisis Type, and Prime Ministerial Rhetoric,” International Studies Quarterly 57, no. 4 (December 2013): 725–37, https://doi.org/10.1111/isqu.12045 .

31 Paul Musgrave and Steven Ward, “The Myth of the Tripwire Effect: Forward Military Deployments and U.S. Public Support for War,” unpublished manuscript, Department of Government, Cornell University, September 2018.

32 There is non-survey work on how decisions to abandon a formal treaty ally can harm a state’s ability to form subsequent alliances. See Mark J. C. Crescenzi, Of Friends and Foes: Reputation and Learning in International Politics (Oxford: Oxford University Press, 2018).

33 On faits accomplis , see Dan Altman, “By Fait Accompli, not Coercion: How States Wrest Territory from Their Adversaries,” International Studies Quarterly 61, no. 4 (December 2017): 881–91, https://doi.org/10.1093/isq/sqx049 ; and Dan Altman, “The Evolution of Territorial Conquest After 1945 and the Limits of the Territorial Integrity Norm,” International Organization 74, no. 3 (Summer 2020): 490–522, https://doi.org/10.1017/S0020818320000119 .

34 Altman, “Evolution,” 497.

35 Schelling, Arms and Influence , 66.

36 On how aggressors can redirect the economic resources of captured territory to boost their own military power, see Peter Liberman, Does Conquest Pay? The Exploitation of Occupied Industrial Societies (Princeton, NJ: Princeton University Press, 1998).

37 Dan Reiter and Allan C. Stam, Democracies at War (Princeton, NJ: Princeton University Press, 2002).

38 Marc Trachtenberg, History and Strategy (Princeton, NJ: Princeton University Press, 1991), esp. 193, 219; and Marc Trachtenberg, A Constructed Peace: The Making of the European Settlement, 1945–1963 (Princeton, NJ: Princeton University Press, 1999), 86–87.

39 Quoted in Hope M. Harrison, Driving the Soviets Up the Wall: Soviet-East German Relations 1953–1961 (Princeton, NJ: Princeton University Press, 2005), 124.

40 Harrison, Driving , 201. See also Trachtenberg, A Constructed Peace , 251–52, 323; Vladislav M. Zubok, “Khrushchev and the Berlin Crisis (1958–1962),” Woodrow Wilson International Center for Scholars, Cold War International History Project working paper #6, May 1993, https://www.wilsoncenter.org/sites/default/files/media/documents/publication/ACFB7D.pdf .

41 For a recent detailed analysis of NATO’s “Enhanced Forward Presence” in the eastern part of the alliance, see Alexander Lanoszka, Christian Leuprecht, and Alexander Moens, eds., Lessons from the Enhanced Forward Presence, 2017-2020 , NATO Defence College Research Paper No. 14, Nov. 30, 2020, https://www.ndc.nato.int/news/news.php?icode=1504 .

42 Michael O’Hanlon and Christopher Skaluba, “A Report from NATO’s Front Lines,” The National Interest , June 10, 2019, https://nationalinterest.org/feature/report-natos-front-lines-62067 .

43 Sebastian Roblin, “NATO vs Russia: A Massive Wargame Is Simulating What Would Happen if Putin Invaded Norway,” The National Interest , Oct. 27, 2018, https://nationalinterest.org/blog/buzz/nato-vs-russia-massive-wargame-simulating-what-would-happen-if-putin-invaded-norway-34497 .

44 O’Hanlon and Skaluba, “A Report from NATO’s Front Lines.”

45 Alexander R. Vershbow and Philip M. Breedlove, “Permanent Deterrence: Enhancements to the U.S. Military Presence in North Central Europe,” Atlantic Council, Feb. 7, 2019, 30–31, https://www.atlanticcouncil.org/in-depth-research-reports/report/permanent-deterrence/ .

46 David A. Shlabak, and Michael W. Johnson, Reinforcing Deterrence on NATO's Eastern Flank: Wargaming the Defense of the Baltics (Santa Monica, CA: RAND, 2016), https://www.rand.org/pubs/research_reports/RR1253.html . For a critique of this study, see Michael Kofman, “Fixing NATO Deterrence in the East Or: How I Learned to Stop Worrying and Love NATO’s Crushing Defeat by Russia,” War on the Rocks , May 12, 2016, https://warontherocks.com/2016/05/fixing-nato-deterrence-in-the-east-or-how-i-learned-to-stop-worrying-and-love-natos-crushing-defeat-by-russia/.

47 It is possible that more substantial deployments of troops could also bolster the credibility of a deterrent threat, if such deployments constitute a credible “sunk costs” signal.

48 On the contributions of quantity, technology, and strategy to military effectiveness and deterrence, see Stephen Biddle, Military Power: Explaining Victory and Defeat in Modern Battle (Princeton, NJ: Princeton University Press, 2004); and John J. Mearsheimer, Conventional Deterrence (Ithaca, NY: Cornell University Press, 1983).

49 Forward-deployed nuclear weapons could also serve this function, though one study found that nuclear forward deployments do not bolster deterrence success (Fuhrmann and Sechser, “Signaling”).

50 Mearsheimer, Conventional Deterrence , esp. chap. 7.

51 Paul Poast, Arguing About Alliances: The Art of Agreement in Military-Pact Negotiations (Ithaca, NY: Cornell University Press, 2019).

52 Kenneth N. Waltz, “A Strategy for the Rapid Deployment Force,” International Security 5, no. 4 (Spring 1981): 67, https://www.jstor.org/stable/2538713?seq=1 .

53 Mearsheimer, Conventional Deterrence , 64.

54 Reiter and Stam, Democracies at War , chap. 6.

55 Lien-Hang T. Nguyen, Hanoi’s War: An International History of the War for Peace in Vietnam (Chapel Hill, NC: University of North Carolina Press, 2012).

56 Mearsheimer, Conventional Deterrence .

57 Ernest R. May, Strange Victory: Hitler’s Conquest of France (New York: Gardner’s, 1999). See also the September 2019 remarks by Pascal Heyman, the Belgian Permanent Representative to NATO. Pascal Heyman, Twitter post, Sept. 3, 2019, 2:22am, https://twitter.com/PascalHeyman/status/1168786332572893184 .

58 Tanner Greer, “Taiwan Can Win a War with China,” Foreign Policy , Sept. 25, 2018, https://foreignpolicy.com/2018/09/25/taiwan-can-win-a-war-with-china/ .

59 Quoted in Kathryn Weathersby, “New Findings on the Korean War,” Cold War International History Project Bulletin , no. 3 (Fall 1993): 15, https://www.wilsoncenter.org/sites/default/files/media/documents/publication/CWIHPBulletin3.pdf .

60 Quoted in Kathryn Weathersby, “Korea, 1949-50: To Attack or Not to Attack? Stalin, Kim Il Sung, and the Prelude to War,” Cold War International History Project Bulletin no. 5 (Spring 1995): 8, https://www.wilsoncenter.org/sites/default/files/media/documents/publication/CWIHP_Bulletin_5.pdf .

61 Weathersby, “Korea, 1949-50,” 5. This estimate was not wholly inaccurate. There were some 16,000 U.S. forces in South Korea in December 1948, after which the U.S. government began to plan the drawdown of U.S. forces there. James F. Schnabel, The United States Army in the Korean War, Policy and Direction: The First Year (Washington, DC: Center of Military History, US Army, 1972), 30.

62 Quoted in Kathryn Weathersby, “Stalin and the Korean War,” in Origins of the Cold War: An International History , second ed., ed. Melvyn P. Leffler and David S. Painter (New York: Routledge, 2005), 270.

63 Kathryn Weathersby, “‘Should We Fear This?’ Stalin and the Danger of War with America,” Woodrow Wilson International Center for Scholars, Cold War International History Project, Working Paper No. 39 (2002), 21, https://www.wilsoncenter.org/sites/default/files/media/documents/publication/ACFAEF.pdf .

64 “Telegram from Gromyko to Tunkin at the Soviet Embassy in Pyongyang,” September 11, 1949; and “Telegram from Tunkin to the Soviet Foreign Ministry in Reply to 11 September Telegram,” Sept. 14, 1949, Wilson Center Digital Archive, accessed May 25, 2021, https://digitalarchive.wilsoncenter.org/search-results/1/%7B%22search-in%22%3A%22all%22%2C%22term%22%3A%22tunkin%22%7D?recordType=Record .

65 Charles Burton Marshall Oral History Interview with Niel M. Johnson, June 21, 1989 and June 23, 1989, Truman Library, accessed May 25, 2021, https://www.trumanlibrary.gov/library/oral-histories/marshall .

66 Shen Zhihua, “Sino-Soviet Relations and the Origins of the Korean War: Stalin’s Strategic Goals in the Far East,” Journal of Cold War Studies 2, no. 2 (Spring 2000): 52, https://muse.jhu.edu/article/9152 .

67 Quoted in Weathersby, “Korea, 1949–50,” 9.

68 Zhihua, “Sino-Soviet Relations,” 63.

69 Quoted in Weathersby, “‘Should We Fear This?’” 10. This is consistent with the recollection of Nikita Khrushchev, who was physically present at the Stalin-Kim meeting: “[I]f everything were done quickly … then U.S. intervention would be ruled out; the United States would not try to intervene with its armed forces.” Sergei Khrushchev, ed., Memoirs of Nikita Khrushchev , Volume 2: Reformer (1945–1964) , trans. George Shriver (University Park, PA: Pennsylvania State University Press, 2006), 92. See also William Stueck, Rethinking the Korean War: A New Diplomatic and Strategic History (Princeton, NJ: Princeton University Press, 2002), 74.

70 Quoted in Weathersby, “‘Should We Fear This?’” 10.

71 Weathersby, “‘Should We Fear This?’” 14.

72 “Ciphered Telegram No. 34691 from Feng Xi [Stalin] to Soviet Ambassador in Pyongyang Shtykov,” July 1, 1950, History and Public Policy Program Digital Archive, Wilson Center, https://digitalarchive.wilsoncenter.org/document/110687.pdf?v=b936d0b235200d206d07eca96e839700 . The report of American bombers and casualties can be found in “Telegram, Shtykov to CDE. Gromyko,” June 30, 1950, Digital Archive, Wilson Center, https://digitalarchive.wilsoncenter.org/document/114911 .

73 Weathersby, “‘Should We Fear This?’” 11; Sergei N. Goncharov, John W. Lewis, and Xue Litai, Uncertain Partners: Stalin, Mao, and the Korean War (Stanford, CA: Stanford University Press, 1993), 101; and Dean Acheson “Speech on the Far East,” Jan. 12, 1950, Teaching American History, accessed May 25, 2021, https://teachingamericanhistory.org/library/document/speech-on-the-far-east/ .

74 Walter R. Waggoner, “Acheson Says U. S. Counts on Chinese Anger at Soviet for Land Seizures in North,” New York Times , Jan. 13, 1950, 1, 2.

75 Goncharov, Lewis, and Litai, Uncertain Partners , 151.

76 Quoted in Odd Arne Westad, “Fighting for Friendship: Mao, Stalin, and the Sino-Soviet Treaty of 1950,” Cold War International History Project Bulletin , nos. 8-9 (Winter 1996/97): 232–33, https://www.wilsoncenter.org/sites/default/files/media/documents/publication/CWIHP_Bulletin_8-9.pdf .

77 Kim Donggil, “Stalin’s Korean U-Turn: The USSR’s Evolving Security Strategy and the Origins of the Korean War,” Seoul Journal of Corean Studies 24, no. 1 (June 2011): 96, https://www.researchgate.net/publication/298957606_Stalin's_Korean_U-Turn_The_USSR's_Evolving_Security_Strategy_and_the_Origins_of_the_Korean_War .

78 James I. Matray, “Dean Acheson’s Press Club Speech Reexamined,” Journal of Conflict Studies 22, no. 1 (Spring 2002), https://journals.lib.unb.ca/index.php/jcs/article/view/366/578 .

79 The plan was contained in his memorandum “War Against France.”

80 Fritz Fischer, Germany’s Aims in the First World War (New York, Norton, 1967), 100.

81 Terence Zuber questioned the existence of the Schlieffen Plan in Inventing the Schlieffen Plan: German War Planning, 1871–1914 (Oxford: Oxford University Press, 2002). The Zuber thesis has come under heavy criticism from historians. See Hans Ehlert, Michael Epkenhans, and Gerhard P. Gross, eds., The Schlieffen Plan: International Perspectives on the German Strategy for World War I , trans. David T. Zabecki (Lexington, KY: University Press of Kentucky, 2014). However, Zuber himself recognized that German strategy called for “the main body to advance through Belgium and Luxembourg into France.” See Inventing the Schlieffen Plan , 259.

82 John C. G. Röhl, Wilhelm II: Into the Abyss of War and Exile 1900-1941 , trans. Shelia de Bellaigue and Roy Bridge (Cambridge: Cambridge University Press, 2014), 325.

83 Quoted in Annika Mombauer, “German War Plans,” in War Planning 1914 , ed. Richard F. Hamilton and Holger H. Herwig (Cambridge: Cambridge University Press, 2010), 61.

84 Critics of our argument may propose that the political impossibility of such deployments makes such discussion moot. Our theory turns not on the political viability of a troop deployment, but rather on its military effects, and the process tracing evidence in this case clearly indicates that such deployments would have deterred Germany. Further, understanding the military advantages of pre-deployment and alliance more generally can overcome even traditional neutrality. Neutral countries that were invaded during the world wars joined alliances after wars’ ends. Dan Reiter, Crucible of Beliefs: Learning, Alliances, and World Wars (Ithaca, NY: Cornell University Press, 1996).

85 Quoted in Gerhard Ritter, The Schlieffen Plan: Critique of a Myth (London: Oswald Wolff, 1958), 161.

86 Fritz Fischer, War of Illusions: German Policies from 1911 to 1914 , trans. Marian Jackson (New York: Norton, 1975), 390.

87 Gerhard Ritter, Sword and the Scepter: The Problem of Militarism in Germany, Vol.2: The European Powers and the Wilhelminian Empire, 1890–1914 , trans. Heinz Norden (Coral Gables, FL: University of Miami Press, 1970), 207.

88 Fischer, War of Illusions , 390.

89 Quoted in Ritter, The Schlieffen Plan , 176.

90 Quoted in Ritter, The Schlieffen Plan , 186.

91 Quoted in Ritter, The Schlieffen Plan , 166.

92 Scott D. Sagan, “1914 Revisited: Allies, Offense, and Instability,” International Security 11, no. 2 (Fall 1986): 170–71, https://www.jstor.org/stable/2538961?seq=1 .

93 Annika Mombauer, Helmuth von Moltke and the Origins of the First World War (Cambridge: Cambridge University Press, 2001), 96–97; and L. C. F. Turner, “The Significance of the Schlieffen Plan,” in The War Plans of the Great Powers , ed. Paul M. Kennedy (London: George Allen & Unwin, 1979), 212

94 Ulrich Trumpener, “War Premeditated? German Intelligence Operations in July 1914,” Central European History 9, no. 1 (March 1976): 80, https://doi.org/10.1017/S0008938900018094 .

95 John Keegan, The First World War (New York: Knopf, 1999), 80–82.

96 Terence Zuber, Ten Days in August: The Siege of Liège 1914 (Stroud, UK: Spellmount, 2014), 31; and Barbara W. Tuchman, The Guns of August (New York: Bantam, 1962), 198.

97 Quoted in Fischer, Germany’s Aims , 37.

98 Quoted in Ritter, The Schlieffen Plan , 166.

99 Tuchman, Guns of August , 203.

100 Mombauer, “German War Plans,” 67.

101 “Lieutenant-Colonel N. W. Barnardiston to Major-General J. M. Grierson,” March 30, 1906, in British Documents on the Origins of the War, Vol. III (London: Her Majesty’s Stationery Office, 1928), 197.

102 “Lieutenant-Colonel N. W. Barnardiston to Major-General J. M. Grierson,” March 31, 1906, in British Documents on the Origins of the War, Vol. III , (London: Her Majesty’s Stationery Office, 1928), 199. Italics in original.

103 “Lieutenant-Colonel N. W. Barnardiston to Major-General J. M. Grierson,” 199.

104 Samuel R. Williamson, Jr., The Politics of Grand Strategy: Britain and France Prepare for War, 1904–1914 (Cambridge, MA: Harvard University Press, 1969), 66. There was a major battle between British and German troops at Mons, Belgium, in late August 1914. The British lacked the fortifications present at Liège and suffered defeat.

105 Daniel H. Thomas, The Guarantee of Belgian Independence and Neutrality in European Diplomacy, 1830’s–1930’s (Kingston, R.I.: D. H. Thomas Publishing, 1983), 461.

106 Williamson, Politics of Grand Strategy , 97.

107 Quoted in David Stevenson, “Battlefield or Barrier? Rearmament and Military Planning in Belgium, 1902–1914,” International History Review 29, no. 3 (September 2007): 503, https://doi.org/10.1080/07075332.2007.9641133

108 Stevenson, “Battlefield or Barrier?” esp. 501, 505–06; Mombauer, Moltke , 162–63.

109 Luigi Albertini, The Origins of the War of 1914, Vol. 2 , trans. Isabella M. Massey (London: Oxford University Press, 1952), 514. See also Sagan, “1914 Revisited,” 171.

110 For an argument that the German military held very strong control over decision-making, see Martin Kitchen, “Civil-Military Relations in Germany During the First World War,” in The Great War, 1914–18: Essays on the Military, Political and Social History of the First World War , ed. R. J. Q. Adams (London: MacMillan, 1990); and Jack Snyder, “Civil-Military Relations and the Cult of the Offensive, 1914 and 1984,” International Security 9, no. 1 (Summer 1984): 108–46, https://www.jstor.org/stable/2538637?seq=1 . For a different perspective on the role of the Kaiser, see Röhl, Wilhelm II . See also Holger Afflerbach, “Wilhelm II as Supreme Warlord in the First World War,” War in History 5, no. 4 (November 1998): 432, 432n, https://doi.org/10.1177%2F096834459800500403 .

111 Marc Trachtenberg argues that Germany did not care about British neutrality and that it would have invaded regardless. See Jack S. Levy, Thomas J. Christensen, and Marc Trachtenberg, “Correspondence: Mobilization and Inadvertence in the July Crisis," International Security, 16, no. 1 (Summer 1991): 189–203, https://www.jstor.org/stable/2539055?seq=1 . Dale Copeland makes a similar point in The Origins of Major War (Ithaca, NY: Cornell University Press, 2000), 84–85. These critiques are not problematic for our argument. These arguments are based on the assumption that British intervention would be too late to save Belgium. This would no longer be valid if Britain had pre-deployed troops.

112 Paul K. Huth, Extended Deterrence and the Prevention of War (New Haven, CT: Yale University Press, 1988), 198n; and Mombauer, “German War Plans,” 66.

113 Mombauer, Moltke , 209.

114 Mombauer, Moltke , 209; and Annika Mombauer, “A Reluctant Military Leader? Helmut von Moltke and the July Crisis of 1914,” War in History 6, no. 4 (October 1999): 439, https://doi.org/10.1177/096834459900600403 .

115 “Memo from Helmut von Moltke,” Dec. 21, 1912, in Der Weltkrieg 1914-1918. Kriegsrüstung und Kriegswirtschaft,  Vol. 1 : Die militärische, wirtschaftliche und finanzielle Rüstung Deutschlands von vor der Reichsgründung bis zum Ausbruch des Weltkrieges + Anlagen (Berlin: Reichsarchiv (Abteilung 3), 1930), 156–74. Thanks to Stefano Jud for translation from the original German.

116 Quoted in Mombauer, Moltke , 221. See also pages 155 and 164.

117 Quoted in Ritter, Schlieffen Plan , 166.

118 Mombauer, Moltke , 221.

119 Mombauer, “Reluctant Military Leader,” 443.

120 Eugene Gholz, Daryl G. Press, and Harvey M Sapolsky, “Come Home America: The Strategy of Restraint in the Face of Temptation,” International Security 21, no. 4 (Spring 1997): esp. 33n, https://www.jstor.org/stable/2539282?seq=1 .

121 Hans Binnendijk, “The Folly of a NATO Troop Withdrawal Decision,” Defense News , June 9, 2020, https://www.defensenews.com/opinion/commentary/2020/06/09/the-folly-of-a-nato-troop-withdrawal-decision/ .

122 Quoted in Breedlove and Vershbow, “Permanent Deterrence,” 2.

123 Tobin Harshaw, “The Future of Nuclear Weapons and the Next Great War,” Bloomberg , Jan. 12, 2019, https://www.bnnbloomberg.ca/the-future-of-nuclear-weapons-and-the-next-great-war-1.1197360 .

124 James K. Wither, “Svalbard: NATO’s Arctic ‘Achilles’ Heel,” RUSI Journal 163, no. 5 (2018): 28–37, https://doi.org/10.1080/03071847.2018.1552453

125 Andrew F. Krepinevich, Jr., “How to Deter China: The Case for Archipelagic Defense,” Foreign Affairs 94, no. 2 (March/April 2015): 78–86, https://www.foreignaffairs.com/articles/china/2015-02-16/how-deter-china .

126 James E. Fanell and Kerry K. Gershaneck, “White Warships and Little Blue Men: The Looming ‘Short, Sharp War’ in the East China Sea Over the Senkakus,” Project 2049 Institute, March 30, 2018, https://project2049.net/2018/03/30/white-warships-and-little-blue-men-the-looming-short-sharp-war-in-the-east-china-sea-over-the-senkakus/ .

127 For example, see Michael J. Mazarr, et al., What Deters and Why: Exploring Requirements for Effective Deterrence of Interstate Aggression (Washington, DC: RAND, 2018), e.g., 37, https://www.rand.org/pubs/research_reports/RR2451.html .

128 On the ability of U.S. forces to contribute to conventional deterrence missions in South Korea, see Michael J. Mazarr et al., The Korean Peninsula: Three Dangerous Scenarios (Washington, DC: RAND, 2018), https://www.rand.org/pubs/perspectives/PE262.html .

129 Richard C. Bush, “Okinawa and Security in East Asia,” Brookings Institute, March 10, 2010, https://www.brookings.edu/on-the-record/okinawa-and-security-in-east-asia/ .

130 Virginia Page Fortna, “Interstate Peacekeeping: Causal Mechanisms and Empirical Effects,” World Politics 56, no. 4 (July 2004): 481–519, https://doi.org/10.1353/wp.2005.0004 .

131 “Most Americans Don’t Support Higher Defense Spending,” Yahoo! Finance , April 1, 2019, https://finance.yahoo.com/news/most-americans-don-t-support-221355051.html .

132 Missy Ryan, “Military Faces Another Potential Coronavirus Toll: Budget Cuts,” Washington Post , May 15, 2020, https://www.washingtonpost.com/national-security/military-faces-another-potential-coronavirus-toll-budget-cuts/2020/05/14/ae7abbf6-906b-11ea-8df0-ee33c3f5b0d6_story.html .

133 Brett V. Benson, Constructing International Security: Alliances, Deterrence, and Moral Hazard (Cambridge: Cambridge University Press, 2012); John Glaser, “Withdrawing from Overseas Bases: Why a Forward-Deployed Military Posture Is Unnecessary, Outdated, and Dangerous,” CATO Institute, July 18, 2017, https://www.cato.org/publications/policy-analysis/withdrawing-overseas-bases-why-forward-deployed-military-posture ; and Fjelstul and Reiter, “Explaining Incompleteness.”

134 Alexander Lanoszka and Michael Hunzeker, “The Efficacy of Landpower: Landpower and American Credibility,” Parameters 45, no. 4 (2016): 18, https://openaccess.city.ac.uk/id/eprint/15415/1/HunzekerLanoszkaParameters.pdf .

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Tripped Up About Tripwires

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American security policy has made use of tripwire forces for many years.  One of the most prominent examples was the case of Berlin: As Thomas Schelling famously described the logic, the small garrison of U.S. soldiers stationed there during the Cold War weren’t militarily capable of defeating the far-larger East German or Soviet forces nearby but, the East Germans or Soviets would be deterred from attacking because any attack would result in the deaths of that small U.S. force, drawing America into a conflict. Our guests, Professor Dan Reiter of Emory University and Professor Paul Poast of the University of Chicago, argue that Schelling was wrong. Their article, “The Truth About Tripwires: Why Small Force Deployments Do Not Deter Aggression,” in Vol 4, Iss 3 of TNSR, argues that deterrence relies almost exclusively on the military value of force deployment, so small token deployments are unlikely to deter a determined attacker.  They illustrate their argument with two cases from the Korean peninsula, and a counterfactual example from World War I.

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Retrotechtacular: Wire Splicing The Army Way

For those of us who started experimenting with electricity when we were very young, one of the essential first skills was learning how to twist wires together. It seems like there’s not much to learn, but after a few failed attempts with nothing but your fingers, you learned a few tricks that are probably still with you to this day. It’s not surprising, then, that there’s an official US Army way to twist wires together, as this Signal Corps training film from 1941 shows.

Considering that the Signal Corps had nearly 80 years of experience with wiring battlefield communications at the outbreak of World War II, their methods were pretty solid, as were their materials. The film mainly concerns the splicing together of rolls of type W110-B field wire, used by the Signal Corps to connect command posts to forward positions, observation posts, and the rear echelons. More often than not laid directly upon the ground, the wire had to be tough, waterproof, and conductive enough that field telephone gear would still work over long loop lengths. As such, the steel-reinforced, rubber-and-fabric clad cable was not the easiest stuff to splice. Where we might cringe at the stresses introduced by literally tying a conductor in knots, it was all part of the job for the wire-laying teams that did the job as quickly as possible, often while taking enemy fire.

The film also has a section on splicing a new line into an existing, in-service circuit, using a T-splice and paying careful attention to the topology of the knots used, lest they come undone under stress. It’s fascinating how much thought was put into something as mundane as twisting wires, but given the stakes, we can appreciate the attention to detail.

31 thoughts on “ Retrotechtacular: Wire Splicing The Army Way ”

These retrotechtacular videos are one of my favorite things. Thanks for digging these up!

“Periscope Films” on YouTube is very dangerous. When I first noticed that channel it cost me at least 50 hours. I just could not stop watching. Instantly hooked I was.

It’s “PeriscopeFilm” https://www.youtube.com/user/PeriscopeFilm/videos

What’s really odd/infuriating is that they add the timecode onto the film themselves. That isn’t present on any of the original film prints.

Maybe so you can easily place an order for the original film

Since an army, especially a conscript army, can get all kinds of people in it’s ranks from geni to ignorami they have to gear their training to teaching monkeys how to play concertos, so it tends to be good.

You could have an army of nobel prize winners and you would still have to train them on the “army way”. it is not a question of intelligence, it is a question of coordination and uniformity. In theory people can fix and repair things “as they see fit” but this equipment must be maintained by others so it is vital to fix things in a prescribed manner. This is life-and-death equipment, your comparison to playing music is comical.

But when you are up to your rear end in alligators, hacking is a valuable skill.

You’re right. A genius could figure out how to do something but if nobody else knows how he did it or how to repair it it is pretty useless to a large organization.

The point is, there are often many different ways to accomplish a given task, but there is only one correct way to accomplish it. The Army way.

There are reasons for this, but the most obvious one is that you may not be alive to explain to the next guy what your novel solution is or how to PMCS it. Figuring out what the last guy did takes time, that time can get you or others killed.

Hey, there’s no such thing as a perfect analogy ;)

Smarts does not often mean mechanical smarts. I remember being in Grad school with a control systems genius who could barely turn a wrench so to speak. Both of us got ME degrees.

Yes, absolutely. Beware the engineer who harbors a delusion of generalized expertise and intelligence. The one who thinks that since he’s very smart in one field, he knows the best solutions in all fields. That man will fix essential systems with the most awful, ignorant kludges imaginable and what’s worse, he won’t recognize them as kludges at all. He’ll put lives in danger everywhere he goes. It’s closely related to the engineer-as-savior syndrome.

From my expirience IT engineers, lawyers and doctors are worst at this. They are usually very smart people with impressive loads of knowledge in their fields but dear god have mercy when they step outside of their fields.

And there are no idiots who truly f*ck things up?

Raise your hands if you’ve ever poked your fingers with the steel strands of Army Signal wire! DAMHIKT

Yeah just from my experience with steel bicycle cables, I *felt it* when he said to leave the insulation on the tip to hold the strands together!

Yeah, underrated and genius move right there. I felt like that was a golden moment of the video for anyone who didn’t already know to do that. It’s sure nice to work with copper most of the time, but same experiences here with Bowden cables (and not the 3d printer kind!). Sometimes a freshly-snipped steel braid can really get you. Ooof, right up under the nail bed. It’ll teach a lesson that will live for a long time. Builds character, but it’s better to just learn proper technique :)

Yup. Even more fun is what happens when you put your hand down on the trimmings, if you’re fast enough it’ll fishhook on you. I did it once in a scramble to get out of a shelter truck. Hours of entertainment.

Poked my fingers countless times with this cable. Had an interesting cornea on my fingers after connecting countless cables.

This 288 page May 1960 U.S. Army field manual is the “Bible” when it comes to Field Wire management. It has lots about splicing, and much more:

“FM 24-20-Field Wire and Field Cable Techniques”

https://archive.org/details/FM24-20FieldWireandFieldCableTechniques

Direct .pdf download:

https://archive.org/download/FM24-20FieldWireandFieldCableTechniques/FM%2024-20-Field%20Wire%20and%20Field%20Cable%20Techniques.pdf

splicing wire is serious when some grunt is going to be pulling on it with all their strength to lay it down or roll it back up. making a good electrical connection is easy, making it mechanically strong at the same time is harder.

You forgot to mention when they go out of their way to drive an LMTV over it. No matter how careful you are, no matter how well you secure it, some idiot is gonna find a way to park something on top of it. Wire is magic that way.

If someone has to risk their life to go splice a wire that got broken in combat, you *really* need to be sure it’s as strong and functional as the original, undamaged wire. Having to do it twice is not good.

And here I am now imagining what it would be like to get sent up over the trenches or whatnot and find a wire that had just come undone from a lazy splice, courtesy of the last lineman. Oooo that would get me boiling mad…

But knowing the way things work in the field, more often than not people probably looked out for their fellows even better than they’d look after themselves. I always remember the story of trench foot in the first world war. How people would be so tired and shell-shocked that they’d fall asleep without taking off their boots and damp socks in the bottom of a muddy, half-flooded trench for weeks on end, causing them to get gangrene and their legs would rot off. The military would try again and again to teach people the dangers and how to properly avoid it, but nothing stuck because they were just so dead-tired and traumatized that a leg rotting off just wasn’t high up on the mental priority list.

So eventually somebody had the genius idea of not telling soldiers to look after their own feet at all. They had the responsibility to look after the feet of the guy next to them instead. And would you believe it—trench foot, as a condition, disappeared overnight. Cases went to zero. Bam. Turns out people really are inherently good and care more about their brethren than their own life and limb. People can seem mean and selfish in our mundane, safe, daily lives… But when it really counts, humans come together and pull through gloriously. It’s one of the most inspiring and morale-boosting stories I’ve ever heard, but maybe it’s just me. And this is coming from a hard-core cynic, by the way. I guess pessimism really is just optimism scorned. But people are certainly good at the end of the day. I truly believe it.

>Turns out people really are inherently good and care more about their brethren than their own life

Not so for the general public who don’t go to the same intensive training to build a team. It’s a life or death situation, but there are selfish idiots break rules for social distancing and not wearing a mask.

When I was a kid the ham old timers taught me to do the Western Union splice. https://en.m.wikipedia.org/wiki/Western_Union_splice

Dunk it in a solder pot and you’ve got a NASA splice. I once worked for this guy who forbade any of his underlings from using opaque heat-shrink, so nobody could hide their shame. I still kind of prefer clear heat-shrink for that reason. It’s nice to see what’s going on in there. And electrical tape holds a place of deep hatred in my heart if it’s used anywhere other than nipples. I will throw a motorcycle wiring harness wrapped end-to-end in electrical tape straight into the trash rather than try to reverse-engineer it and build my own electrical system from the ground up instead. Damn them to hell.

That’s a trait I’ve found frequently in certain professional fields. They’ve received training in the aspects of IT that are relevant to their profession, such as medical diagnostics, avionics, industrial control systems, etc. Expert training. Detailed training. They’re also highly competent and skilled in those areas.

They are not highly trained, skilled, or experts outside their specialty, or in IT generally. But some of them like to think they are, and it’s irritating to have to re-educate them.

That reminds me of a fellow I knew many years ago. He’d bought a Ducati 450 single from a guy in the RAAF. Said previous owner had replaced the wiring harness, but not with colour-coded wiring. He’d replaced it with Air Force wiring, which (at that time, at least) was all white, with number coding.

He had to re-replace the harness with the correct colour coded wiring, to match the wiring diagram in the manual

The Navajo Code Talkers were also trained as signal corp. They laid the lines down in battle. Iwo Jima was particularly brutal – most of the fighting was within 100 yards or closer. They had to constantly shift position, thus had to move the forward posts each time.

Imagine making these splices in battle, lying on the ground, in the mud, with all of the noise and chaos of battle. I assume the training included that kind of experience to prepare the men. Those conditions were nothing like the ones in the training movie. Add to that if it was cold, like the Marines at the Frozen Chosin. Wearing gloves would add to the effort.

Can some of the posters above elaborate? The comments by some tell me they did this in the Army or other branches.

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Wire and linemen for messages.

Army radar on the M.S. Nordic protecting the Panama Canal in 1942 [above] was designed at Camp Evans.[/caption]By Fred Carl

One of the keys to victory in modern warfare is making sure information about battle conditions gets to command. This way command can direct reinforcements of soldiers and supplies where they can help most.   This is the mission of the U.S. Army Signal Corps, getting the message through.  During the civil war flags, scouts and horse-mounted messengers were the carriers of communications.  During WWI wireless and telephones were employed.  During WWII radio, radar and telephones were used.   During the Gulf wars radio, radar and satellites were and are the cutting edge communications tools.

As a WWII Signal Corps laboratory, Camp Evans supported the Signal Corps mission with “phenomenal” radio, radar and countermeasures developments.   As important as radio and radar were to victory, the bulk of WWII communications were done over telephone wires. Camp Evans played a roll in telephone wire equipment development worthy of being recounted in volume III of the official history of the Signal Corps in WWII: “The Signal Corps – The Outcome”.

The device developed in Wall was the MX-301/G.  It is described as “indeed one answer to wireman’s prayers” It was a high-speed telephone wire dispenser. It could lay wire silently, rapidly, and without dangerous rotating reels.  It was originally designed for laying wire from an aircraft at speeds up to 110 miles per hour.  In the field linemen found they could adapt the device to lay wire from a backpack, vehicles traveling 60 miles an hour, or even shoot wire out using bazooka rockets.

The rapid dispensing of wire was very important. General Eisenhower expected to need 500 miles a day of “assault” wire or 67,000 miles a month of all types of wire just in Europe.  In reality, after the D-day invasion breakout, the troops were advancing so quickly there was no time to recover used wire. 75,000 miles of assault wire and 200,000 miles of all wire was used a month.  Without excellent devices to quickly dispense the wire, like the MX-301/G, communications could not have kept up with the troops. In the Pacific theater, the dense jungles made a formidable barrier to easy communications setup. Once the wire was dispensed the wire had to be elevated onto poles or palm trees to prevent vehicles or tanks from cutting the wires.

Wall resident, Mr. Warren Cochran, was a lineman in the Pacific.   He was one of the Signal Corps men who made sure the message got through to help bring about victory.  He was warned by his commanders not to use safety equipment when he climbed a pole to repair a line.  Often the Japanese soldiers would cut the telephone lines, position a sniper, then wait for the U.S. soldier to climb the pole to repair the cut. Your safety equipment would save you from a fall but would keep you from getting down quickly if the sniper missed on his first shot.  Years later as a Bell System employee Mr. Cochran would not face this type of occupational hazard when he helped maintain the secure telephone system at Camp Evans.

Besides snipers and surprise attacks the WWII Pacific theater soldiers had to defend themselves against Japanese soldiers who hid in deep caves. One night the camp Mr. Cochran was sleeping was attacked by a Japanese soldier who possibly hid in a cave waiting to attack U.S. troops.

Right beside, not behind, the soldier in every war in the 20th century was the Signalman.  He was installing or maintaining telephones, radio, or radar in the thick of battle.  These devices were as essential to victory as bullets. Many of these devices were designed right in Wall at Camp Evans.

Camp Evans was called upon to help eliminate the problems of Japanese hidden deep in caves.  The solution was classified, messy and shows the desperation of the problem.  This is a story for another day

page created January 20, 2004 .

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6 DIY Trip Wire Alarms for Off-Grid Security

By Steve Nubie 2 Comments

Estimated reading time: 28 minutes

A lot of folks have never put together a trip wire alarm, and there’s a good reason. There are just not a lot of occasions where a trip wire is necessary. However, when those occasions do emerge, it’s at least worth understanding the concept of what works and what doesn’t.

What Exactly is a Trip Wire?

But who needs them now, do it yourself versus buy it yourself, trip wire 101, electrical wire, monofilament fishing line, bungee cord, lasers, infrared, and motion detectors, rocks in cans, firecracker poppers, .22-caliber blanks, air horns, sirens, and other noise makers, what about light, this is not about the use of lethal force, location, location, location, 1. bungee marbles, 2. monofilament on the rocks, 3. paracord pull-string fireworks, 4. thin wire .22-caliber blank, 5. winter white trip wire, 6. back gate avalanche, is this a good idea.

A trip wire is a long length of thin wire, monofilament fishing line, or any other type of cordage that is usually connected to something that makes noise. The idea is that when an intruder either human or animal steps into the wire, the alarm is sprung, alerting you to an intrusion.

The trip wire concept was developed in wartime as a way to alert troops of an enemy incursion. This was particularly needed at night and was often used in the dense island jungles during the war in the Pacific in World War II.

The usual configuration was a thin length of rope suspended low to the ground between trees with empty C-ration cans filled with stones to rattle the alarm whenever the wire was “tripped.” And while booby traps were sometimes used to maim or kill, there was always the concern that an innocent civilian or friendly soldier wandering off to go relieve himself would trip the wire.

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The usual reason someone considers a trip wire is when they are in an area with the potential for any number of unknown threats. The idea is usually to make noise to signal an intruder .

• The threat could be from wild animals like bears or wolves approaching a camp in a remote area.
• In countries ravaged by civil wars and civil unrest, no night is safe and trip wires are sometimes used to at least alert the local population if a covert threat is approaching.
• Following a disaster , many people find themselves isolated and alone with the potential for looters or worse. That’s when a trip wire may at least scare them off, if not serve as a warning of an unwelcome approach.
• In times requiring a bug-out to a distant but safer location, there are occasions where a night must be spent on the road in unknown territory where the threat is equally mysterious. Trip wires would serve as a perimeter defense to at least alert anyone spending an unplanned night on the road of any approach.
• And yes, they’re still used in war zones, although the technology of trip wires in those areas is usually defined by lasers, electronic signals, or infrared beams connected to electronic alerts through cameras or video or in extreme cases: explosives.
• In fact, the concept of contemporary home security systems connected to motion-detector technology to turn on lights; sound an alarm, record video, or alert the local police are the 21 st century versions of the trip wire concept.

It may seem unnecessary to build your own trip wires when so many options appear on the Internet , but if a situation makes the Internet undependable or unavailable, or deliveries or the purchase of many things is difficult or impossible, that might be a good time to know how to improvise a trip wire.

There’s also the fact that in some instances, the electricity is out or unavailable, and most modern security solutions require at least some level of power. In a worst case scenario with a total grid failure, technology will quickly diminish and old-school, analog solutions will offer the most dependable options. Those are the types of trip wire concepts we’ll cover.

We might as well start with the wire. There are a variety of options . Usually, the wire or cord is low-profile and hard to see. It also needs to be relatively strong. If someone or something walks through the wire or cord and it easily breaks, little is accomplished except alerting the intruder to the fact that you’ve setup some trip wires.

Here are options to consider:

Electrical wire comes in a variety of gauges, but the smallest (and most inexpensive) gauges are referred to as 14 and 16 gauge. They’re more than strong enough to serve as a trip wire.

They’re all coated with a flexible plastic coating that comes in a range of colors. White, black, red, and green are the most common, and those colors present camouflaged, stealth characteristics, depending on the time of year, time of day, and natural surroundings. Floral wire is another option and also comes in a variety of colors.

Fishing line is thin, strong, and also hard to see. Buy one of the heavier weight tests of at least 50 pounds or more. Avoid any of the brightly colored lines. Go with a neutral, plain monofilament.

Paracord is another surprisingly strong option, but you have to think about the color of the cord. During winter, a white Paracord might makes sense if the ground is snow covered. A green or camo cord could work well in a forest or field. Black is an obvious choice for night.

You don’t see bungee cord mentioned in a lot of the write-ups about trip wires, but it has a characteristic that could make sense if you think about it. If the idea of your trip wire is to rattle a bell, cans, or other noise maker, a bungee cord will certainly make that happen.

In fact, a bungee cord may cause more noise to occur than any of the other options we’ve mentioned due to its flexibility and springiness. A black bungee makes sense. Green if you’re in the woods.

If your trip wire is designed to trigger a mechanism, bungee is not the best choice, but if you’re rattling cans the old-fashioned way, it’s a good option.

You can buy these things and improvise a trip wire yourself, but make sure they’re battery or solar powered or have a way to recharge the batteries . These are complicated solutions, so we’ll mention them but we’re not going to spend a lot of time covering ways to make technology work in a primitive environment.

Some websites offer tips and solutions to improvising trip wires with technology, but it’s a lot of work and you have to consider how and when you’ll need any trip wire, and for how long.

The idea of most trip wires is to make a lot of noise when someone trips over the wire. Noise makers vary depending on what you have available or may have bought in advance. We’re going to assume your situation caught you a bit by surprise and that you have to improvise from available materials.

It’s believable that a lot of us would have wire, cords, and fishing line lying, around but things that make noise require a bit of creativity or at least some pre-planning , especially if you require a very loud alarm.

How loud your alarm needs to be depends on your distance from the trip wire and whether you are inside or outside. Someone camping in a tent will be more likely to hear a rattle of rocks in a can than someone sleeping in their home or cabin.

If you are at a distance from your trip wire or indoors, you may need to plan and buy ahead to acquire louder alarms like blank cartridge firing mechanisms, firecracker poppers, air horns, or anything else that will be heard under most circumstances.

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And if you can, paint your alarms to match the environment. If you don’t have paint, you can rub some mud or clay on the bell/can/noisemaker so it is somewhat camouflaged. Black is good at night, camo combos for any natural forest or field, and snow white for winter.

If you’re trying to keep animals at bay, the colors are less of an issue. Animals only see in black and white, but keep an eye on the contrast. They can still notice highly contrasting shades.

A lot of us have bells around for various reasons including cowbells, Christmas bells, antique bells, and collectible bells. And then some of us don’t. If you have any assortment of bells, you’re off to a good start with a trip wire.

Even if you’re not a bell collector, there’s a good chance you have access to tin cans and rocks. No rocks? Anything that makes noise in a can will do from bolts to nuts or better yet, marbles— although marbles may jostle around in your can in the wind, so maybe stick with the pebbles.

You only want a few in the can but enough to make noise when the can is jostled. Smooth, rounded stones and marbles are best. Look for rounded stones in river and creek beds.

Drop a few in and give the can a shake. Adjust until you think you have the most and best noise for a shake. And if you don’t think a rattling can is going to work, then you’ll need to think about stocking some very loud alarms like the next few items.

There’s a type of firework that has two stings emerging from either end of a firecracker. When you pull the stings, the firecracker pops. They’re loud, and you can tie them onto a number of trip wires around your area.

Some of them are made out of paper and will get wet due to rain, snow, or morning dew, so wrap them in plastic cut from a black or neutral garbage bag. They’ll most likely scare off a wild animal and might scare off an intruder. Either way you’ll certainly hear it.

This isn’t about setting up a full loaded .22 caliber round on a trip wire. That’s a really bad idea. Trip wires are indiscriminate and when tripped, the wire fires. Most .22-caliber blanks are used for nail hammers to drive nails and pins into concrete.

The firing mechanism for trip wires and .22 blanks can be bought online , although the blanks are available at most hardware stores next to the nail guns . There are also 12-gauge blank variations on this concept.

As a trip wire, they’re mostly designed to deter wild animals, but the people who sell them offer all sorts of reasons to use them . You’ll certainly hear it, and it will scare most anyone and anything away.

However, it may cause a response you don’t necessarily want. If someone is approaching and they are armed, they may perceive the detonation of a .22-caliber blank round as actual gunfire and return fire. Up to you.

If it makes noise, it’ll work on a trip wire. The only challenge is figuring out how to trigger the noise. Things like sirens need power, but if you’re handy with a little wiring, you can make a trip-switch to set off the siren.

There are also solar powered options available . There’s some advice out there about setting up a rock over an a ir horn that will fall on the air horn button when tripped. That requires some precise setup and once that rock is on the air horn, it’s going to make a lot of noise until you lift the rock.

You’ll also probably use up all the air in the horn by the time you get out of bed or your sleeping bag to lift the rock.

There are solar powered motion detectors that will illuminate an area. These are best hung high in a tree out of sight and out of reach. It’s a variation on the trip wire concept, and it’s usually used to dissuade animals. It could also deter an intruder, but if you’re using something to trip an alarm that will notify you of an intrusion, a light in the night will do little good if you don’t see it while you’re sleeping or otherwise occupied.

Most trip wire concepts are designed to make noise to let you know that someone or something is approaching, and improvising a light to a trip wire can get a little complicated unless you have some good skills with wiring and trip switches. We’re going to skip the lights and stick with noise.

Booby traps have often been used in times of war and they are designed to kill. That’s a really bad idea. The whole idea is to either scare something or someone away with sound or to at least be alerted to the presence of something approaching.

Even a blank .22-caliber cartridge should be pointed towards the ground. Otherwise, the blast could send shrapnel from a tree trunk or branch in someone’s direction, and you don’t want it to be one of your children or an innocent wanderer lost in the night. This is about making noise, not war .

Where you place any trip wire is as important as the design of the trip wire itself. You want it far enough away to give yourself some time to observe the direction of the alarm and see what’s coming plus prepare to respond. But you also want it close enough so you can hear it.

Another location factor is the height of the trip wire from the ground. If you’re concerned about human intruders or large animals like a bear , you’ll want your trip wire about a foot above the ground. 6-inches above the ground is about the minimum or someone or something could step on the wire without tripping it.

Also, if it’s any lower than 6 inches, every random squirrel, raccoon, possum or most any other rodent could trip your wire repeatedly. If that happens enough, you may take to ignoring the trip wire noise while assuming it’s just another passing rabbit when it’s the intruder you were so worried about in the first place.

Support for attaching a trip wire is something else to think about. A lot depends on what’s available at the location and what kind of trip wire you’re using. Two tree trunks could work, but they will create a very taut trip wire that may not ring any bells for long. They could also cause an intruder to literally trip which may be an effective deterrent–or not.

The branches of two trees or two saplings give some flexibility to any trip wire and could result in a sway in the wire, causing the noise to persist a little longer.

Two stakes in the ground are another solution, but if you’re trying to raise your trip wire to a foot of height, you’ll need long and large stakes deeply imbedded in the ground.

The number of trip wires you set up is another location consideration. Think in terms of avenues of approach. Around a home or dwelling, any open area like a gap in a fence, a gate, an open back or front yard, approaches to doors or windows, or approaches to outbuildings are worth thinking about.

A lot depends on what you’re worried about, the location, and the immediate threat level.

A remote survival camp or any campsite for that matter might require a number of trip wire setups, but even then –animals prefer open paths and clear terrain. A human intruder may do otherwise and stick to the cover of scrub, brush, and trees, so you just have to do your best to estimate what could be coming and from where.

Check your trip wires if you have them in place for any length of time. Improvising an alarm with some rocks in a can is a good idea, at least until it rains or freezes and the water or frozen rocks in the can fail to rattle.

It’s also possible one of your trips has worked loose; been tripped without you knowing it, and loose on the ground, or something as simple as a knot that has worked loose. It’s actually somewhat of a “set it and forget it” approach, but it’s worth checking them from time to time if you need them for any duration.

Remove your trip wires when you don’t need them anymore or when you move on. They will cause you or anyone else to trip, including family members, as long as they’re in place. You also may need them again.

The DIY Trip wires

The advantage of a bungee cord as a trip wire is its springiness. Think of it as a rubber band on steroids. In fact, the interior of a bungee cord is just that. Long strands of rubber encased in a flexible fabric braid.

You can attach anything that makes noise to a bungee cord. The advantage is that a bungee will rattle and shake longer while making more noise.

• Bungee cord of sufficient length for your trip wire area. You can buy coiled bungee cord in various colors and cut them to length. If you only have packaged bungee cords of varying lengths with hooks, you can connect them together, although the hooks will be somewhat visible during the day.
• Various soup cans painted to match the terrain or time of day. They should also have holes punched towards the top of the can on either side.

• (You can substitute bells for the cans.)
• Choose a bungee cord color that you think will blend in the best with the surrounding areas.
• Wrap the one end of the bungee around a tree trunk, branch, sapling or stake. Tie it off with two half-hitches and pull tight.
• Thread your can or cans onto the bungee.
• Stretch it tight to another tree trunk, branch, sapling or stake and wrap and knot with two half hitches until tightened.

• Add marbles to the can and test it with a few pulls on the bungee. Add or remove marbles depending on the sound.
• Test your bungee trip wire again with someone in camp or in the house and ask them if they can hear the cans? If not, move the trip wire closer or add some more cans.

Monofilament is an excellent trip wire source. It’s hard to see during the day and totally invisible at night. The key is to have a strong enough weight test to activate the noise without breaking. It can be used in most any trip wire setup in any location.

• Monofilament fishing line.  50 pound test or higher is best, but any weight test will do if it’s all you have on hand. You could even double or triple up the monofilament if you’re worried it will break or snap.
• Empty tin cans. Soup cans are a good size. Peel off any colorful labels and either paint them or coat them in a thin film of mud so they are less reflective. Paint the cans black or do a camo pattern depending on the surrounding area.
• Smooth, round rocks, nuts, bolts, marbles —anything hard that can easily move around and rattle in the can.
• Cordage or wire to attach the cans to the monofilament.
• Wrap the one end of the monofilament around a tree trunk, branch, sapling or stake. Tie it off with an improved clinch knot (a fishing knot perfectly suited to monofilament) and pull tight.
• Punch 4 holes in each can.

The holes should be punched in pairs towards the top of the can about a ½ inch apart and opposite each other at the rim of the can. This is so the can is bound tight to the monofilament as it is threaded through the holes to ensure a good shake.

• Thread the monofilament through the holes.

• Add the can or cans along the monofilament, but try to place them in spots that are obscured by brush, tall grass, or other natural camouflage. It makes no difference at night, but take a look when it’s dark to be sure.
• Stretch it tight to another tree trunk, branch, sapling, or stake and wrap and knot with another improved clinch knot and pull light.
• Try to locate the cans in a location that is hard to see during the day.
• Drop a few rocks in the can and shake the fishing line wire to see if the cans rattle. Add more or less rocks until the cans make a racket. Continue to add cans where you can. Tighten the cans to the monofilament if you need to.
• Test your monofilament trip wire and have someone in camp listen and ask them if they can hear the cans. If not, move the trip wire closer or add more cans.
• Thin paracord . A type I or type II is thin enough to be obscure but strong enough to function as a trip wire. Choose the color that best matches the terrain and time of day.
• Pull-string fireworks. They’re legal to buy in most states and can also be purchased online. You’ll need to have them on hand because they’re very difficult to improvise.
• Choose a paracord color that will blend in with the surrounding area.
• Wrap the one end of the paracord around a tree trunk, branch, sapling, or stake.
• Find a location that is hard to see along the paracord and tie one end of the pull-string firecracker to the cord.
• Tie the other end of the paracord to another tree trunk, branch, sapling, or stake and wrap and knot with two half hitches until tightened.
• Carefully tie the paracord to the other end of the pull-string using a square knot or any knot you can improvise. You have to do this delicately. You want the paracord tight, but you don’t want to accidentally detonate the firecracker. If you want to get the best tight line, you could tie the final end of the paracord to the tree or stake with a trucker’s hitch . This will give you a little more control over the slack, but be gentle.
• You don’t want to test your popper trip wire or you’ll have to retie another one. If you want to test the distance and whether or not you’ll hear it, have someone in camp or in the house listen while you pull a spare popper. If they don’t hear it, move the trip wire closer. Don’t be tempted to add multiple poppers to the same trip wire. What will most likely happen is that one popper will trip, leaving any others unexploded.
• Unlike bells and tin cans, you have to rearm your firecracker trip wire whenever it goes off. That’s not a bad idea to at least see if there are any footprints or paw prints to tell you if your intruder was human or a stray dog.

• Floral wire . Black is the default color, but if you have a green or white color that can match the terrain or time of year (snow), that’s a good idea.
• A .22-gauge firing capsule. You can buy these online. They’re hard to find in stores.
• Blank .22-gauge loads. Buy these online where you bought your firing capsule or at a hardware store in the nail bun aisle.
• Wrap the one end of the wire around a tree trunk, branch, sapling or stake. Choose a color that matches best with the surroundings.
• Attach an unloaded .22-gauge capsule in an obscure spot.
• Attach the other end of the wire to the .22-gauge firing capsule.
• Stretch it to another tree trunk, branch, sapling or stake and pull until you have tension on the .22-gauge firing mechanism.
• Test the unloaded .22-gauge capsule by pushing on the trip wire to see if the pin fires. If not, adjust the tension. If the pin fires, rearm the firing mechanism and carefully add a blank .22-gauge cartridge.
• If appropriate to the situation, do a test. It will be loud and attract a lot of attention. If the firing pin is firing when unloaded, you should be good to go if a test causes local problems or concerns. Anything that sounds like a gun shot in the neighborhood may attract some unwanted attention.

This setup uses a white length of electrical wire attached with overlapping loops through two holes in the top of a can painted white. Obviously, it’s a winter trip wire and it uses marbles or pebbles to create the alarm. The overlap of the wires causes the can to shake and rattle more than a conventional wire or line passing through the holes.

• White electrical wire
• A can or cans painted white
• Marbles or pebbles

Directions:

• Attach one end of the wire to a tree branch.
• Run the wire through the can in a discreet location, but overlap the wires so the can shakes when the wire is tripped.

• Attach the other end of the wire to a branch and test.

If trouble is close to home and you need to come up with a trip wire fast, this is one option. This is a trip wire connected to a gate, causing an avalanche of large rocks to fall onto a large piece of sheet metal or even a metal garbage can. It makes a lot of noise and can also be staged so the rocks fall onto the metal when the gate is pushed rather than pulled open.

You can improvise this kind of setup anywhere someone may enter uninvited, from a barn door to a back door to a door on a wood shed. This is not a stealthy trip wire. It assumes that a gate or other barrier is obstructing any view of the setup.

• Bucket to hold the ro cks.
• About two dozen large rocks from 1 to 2-inches in diameter.
• A large metal surface or object that will make a lot of noise when rocks land on it. Sheet metal, metal garbage cans, metal ductwork, any type of metal that’s relatively thin and will create noise.
• A wood platform 12” square to support the bucket
• Three wooden dowels about 3 feet long. (You can use old broom handles or even 1×2’s can work).
• Cordage . Any type and any color. The trip wire will also be obscured by the gate or barrier.
• Fill your bucket with your rocks and dump them on your metal sheet, can or whatever else your using to assess the noise. Ask someone inside your home or camp to determine if they can hear it.
• If you’re satisfied with the noise level, fill the bucket with your rocks.
• Pound the 3 support sticks into the ground in a triangle that will support the 12” square platform.
• Set the 12” platform on top of the support sticks. You don’t want to drive the support sticks too deep into the ground. You want this to be a precarious balancing act.
• You have two options. If your gate pulls open towards you, attach your trip wire to the gate and to the front support stick or your three sticks setup far enough away to allow the rocks to fall on the metal. Place the metal in the best location for the rocks to fall. You might want to put some rocks under the metal to lift it off the ground to increase the noise and hold it in place to some degree. When the gate is opened, the trip wire will pull out the support and the bucket will fall forward onto the metal.
• If your gate opens away from you, set up the support sticks and the platform right next to the gate. When someone pushes the gate open, it will topple the bucket with the rocks onto your metal plate or can.
• Test either option to see where the rocks fall and place your metal sheet or container in that location.
• Test again and ask someone inside the house to assess the noise level.
• If satisfied, set the trip or add more rocks or adjust the metal location or type of metal. It’s an easy set up and will create enough noise to cause most intruders to jump out of their boots.

Are There Other Approaches?

No doubt . Trip wires have been around a long time, and what you choose to improvise is only limited by your imagination and materials on hand . What we tried to do here was explore the concept so anyone could take the basic idea and adapt it to their needs, available supplies , and their location. It’s all a question of finding stuff that will make a lot of noise when someone trips over your wire.

In an emergency, it’s good to know how to do this stuff. In an ideal scenario, you would have sophisticated electronic devices that are solar powered and connected to motion detectors and all manner of alerts and alarms. Complicating things further is that any device with any level of electronics will also need to be weatherproof.

But this isn’t about an ideal scenario with a house surrounded by lasers . It’s about a sudden and surprising time when things rapidly become dangerous or threatening. Anyone in that situation would have plenty to think about and the ability to quickly improvise something as basic as perimeter alarms with trip wires not only makes sense but simply seems like a good idea. Just don’t throw way any old bells.

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The following is the description for a soldier's drawing sold on eBay, July 20, 2013 by seller urfaust who provided the translation from the original German. 'Original German WW1 signed hand drawn pencil sketch on blank field postcard. It was sent Oct 11 1915. The upper part shows tripwire and barbed wire and the lower part a caltrop. The artist writes some explanation on the reverse side. A short translated part of the writing on the reverse side: "Tripwire: Between barbed wire and trench there are simple wires on a low level hidden in the grass ... storming French who passed the barbed wire ... trips ... for enhancement there are several caltrops around. These things are very cruel. You can throw them in any way but always on sharp top will be upside. They cut right through heavy boots and make soldiers unable to fight. Also storming soldiers may trip at the tripwire and fall with hands right on the caltrop. These barriers are in front of our trenches and then we come. The biggest and most persistent barriers ..."'

Trip wire is a fortification.

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