Peter Brush, "The Story Behind the McNamara Line"


by Peter Brush

(A version of this article appeared in Vietnam magazine, February, 1996, pp. 18-24.)


On September 7, 1967, at a press conference in Washington, DC, United States Secretary of Defense Robert McNamara announced plans for the construction of an electronic anti-infiltration barrier below the Demilitarized Zone (DMZ), the line of demarcation between North and South Vietnam. The principal purpose of this "McNamara Line" would be to sound the alarm when the enemy crossed the barrier. Allied firepower in the form of air and artillery strikes would then be brought to bear upon the People's Army of Vietnam (PAVN, the North Vietnamese Army) in order to curb infiltration from the north.1 The McNamara Line represented an attempt by the US military to merge modern technology with one of the oldest defensive techniques in warfare. The US would learn that more than sophisticated technology was necessary to make an effective barrier.


Organized warfare is older than human history, and artificial barriers for defense even predate the cultivation of plants.2 Both the Great Wall of China and Hadrian's Wall in Britain were constructed to minimize the ability of barbarians from the north to raid into more settled areas.

Similarily, the Vietnamese made use of the barrier concept in the 17th century, when, in 1620, North and South Vietnam began a separate political existence that would last for 150 years. The Nguyen in the South constructed two enormous walls at narrow points near the center of the country. In seven major campaigns, some lasting several years, the Trinh armies from the North never succeeded in breaking through both of these barriers.

These conflicts between the Nguyen and the Trinh contained an element of prophetic significance. The Portuguese and the Dutch were the superpowers of that era. The Dutch were attempting to push their European rivals from Southeast Asia and their foremost rival was the Portuguese. The Dutch supported the Trinh. The Portuguese supported the Nguyen, sending them regular shipments of modern weapons from Portugal. As early as 1615 the Portuguese had constructed a foundry so the Nguyen could produce heavy guns locally.3 These 17th century events portended the superpower rivalry of the Cold War between the US and the Soviet Union, a rivalry which would again be played out in Vietnam.

The French were aware of the successful barriers of the Nguyen in Vietnam. During the First Indochina War, generals considered implementing this barrier concept at the narrow part of Vietnam in order to separate the "rotten" north from the less heavily infected southern part of their colony.4 But the defeat of the French by the Vietnamese communists at Dien Bien Phu rendered France's problems with its recalcitrant colony irrelevant. The Viet Minh victory over the French led to the signing of the Geneva Accords and to the beginning of the end of France's military presence in Indochina.

In 1954, France sent many of its Indochina veterans to Algeria when civil war broke out there. In Algeria the French would fight with a passion that was lacking in Indochina. Algeria was home to one million settlers of European origin who looked to France for protection and France felt a moral obligation to look after their interests. In addition, and unlike Indochina, Algeria was considered to be an integral part of metropolitan France.

The Algerian nationalists (Front de la Liberation Nationale, or FLN) formed two military forces: an "internal" army that operated in Algeria proper and an "external" army that resided in the neighboring states of Tunisia and Morocco. The function of the external army was to provide men and military supplies for the nationalist forces in Algeria. The French military was denied permission by the French government for political reasons to enter into military operations against the external army forces in Tunisia and Morocco . The military situation in Algeria suggested that the situation was ripe for the implementation of the barrier concept.

This barrier, like the Maginot Line before World War II, was named after the minister of defense in office at the time of its construction. The Morice Line in Algeria was completed in 1957 and ran along the Algerian-Tunisian frontier for 460 kilometers and along the Algerian-Moroccan border for 750 kilometers, from the Mediterranean Sea to the barren Sahara Desert. At the core of this barrier was an eight foot high electric fence charged with five thousand volts. On both sides of the fence was a fifty yard area heavily sprinkled with antipersonnel mines. At the edge of the mine fields was a continuous row of barbed wire of the style common on the Western Front in World War I.

The electric fence was designed to kill anyone who came into contact with it. Beyond the barbed wire on the Algerian side, roads were constructed over which passed frequent armed ground patrols equipped with Alsatian tracker dogs to detect and destroy infiltrators who attempted to breach the line. Assault helicopters conducted aerial patrols. Powerful searchlights illuminated the barrier at night. Electronic sensors could determine with precision the location of enemy raiding parties. Radar was situated to automatically sight and fire 105 mm howitzers.

The French manned this barrier with 80,000 combat troops, the strongest concentration of French forces in Algeria. These troops included paratroop regiments, mechanized units, and armored units. Successful night crossings by the Algerian nationalists were usually engaged and destroyed before the end of the following day.

The FLN soldiers tried every means to break through the French barrier. High voltage wire cutters were obtained from Germany. Hooks were employed to lift up the wire to allow troops to pass underneath. Soldiers tried to dig under the wire and to throw insulated materials over it. Bangalore torpedos were used to blast holes through it. Diversions were attempted by small groups setting off the alarms while larger groups attempted to cross in other places. The FLN tried to outflank the line by crossing in the desert sands of the Sahara. In almost all cases, however, the French were able to bring massive firepower against the nationalist soldiers and destroy them. The overwhelming superiority of French airborne troops and the lavish use of transport helicopters usually ensured tactical success for the French and failure for the nationalists. In the first seven months that the Morice Line was operational, the FLN lost 6,000 men and 4,300 weapons.

The Morice Line was successful in reducing infiltration into Algeria by as much as 90 percent. By denying external support to the FLN, the barriers established "a kind of closed hunting preserve" for the French military.5 Any nationalist soldiers who successfully breached the line were dealt with by commandos de chasse, company-sized units composed of French and Algerian troops who pursued the nationalist soldiers wherever they went until they could be located and destroyed. The FLN was forced to end large-scale attempts to breach the barrier. The internal Algerian army was effectively cut off from external support.


From the beginning of the American involvement in Vietnam, The United States recognized that South Vietnam's borders with Laos and North Vietnam were porous and this porosity permitted the infiltration of men and supplies into the South. The idea of an artificial barrier between North and South Vietnam was first considered by the Americans in 1958. In 1961, The head of the US military advisory group, Lieutenant General Lionel McGarr, made a proposal to Secretary McNamara that a cordon sanitaire be created along the Laos-South Vietnam border to prevent infiltration from North Vietnam.6 Another proposal that year was made under the auspices of the Southeast Asia Treaty Organization (SEATO): SEATO Plan 5/61 proposed to physically seal the border across both the DMZ and the panhandle in Laos with an international force.7

General William Westmoreland, the head of US forces in Vietnam, also favored a manned barrier to prohibit infiltration from the DMZ and Laotian panhandle into South Vietnam. In 1964 he recommended an international force be utilized to accomplish this in a proposal to Deputy Ambassador Alexis Johnson. Westmoreland's proposal was to make the barrier part of a regional development project, with engineers, protected by combat troops, extending a road from South Vietnam across the Laotian infiltration routes to the Thai border. In this scenario, the combat troops would function as the infiltration barrier. Officials in Washington showed no enthusiasm and the plan was set aside.8 These early barrier proposals were not rejected outright; rather, they were repeatedly shelved because of the belief that heavy aerial bombing would deal with the problem of infiltration.

By early 1965 it became clear to the Americans that their cautious policy in Vietnam was not working. South Vietnam was at the point of "impending collapse"9 and a continuation of existing policies would necessarily lead to defeat for the US and South Vietnam. The US response was to greatly increase its troop levels in the South (184,000 by the end of 1965; 385,000 by the end of 196610) and to initiate Operation ROLLING THUNDER, the sustained aerial bombing of North Vietnam.

In mid-1966, the US concluded that neither of these policies was effective. US troop increases were matched by increases in the infiltration of North Vietnamese forces into the South. The Pentagon Papers noted that ". . . the total number of individual flights against North Vietnam in Operation Rolling Thunder rose from 55,000 in 1965 to 148,000 in 1966, total bomb tonnage from 33,000 to 128,000, the number of aircraft lost rose from 171 to 318, and direct operational costs rose from $460-million to 1.2- billion." The 1966 bombing ". . . accomplished little more than in 1965."11 Apparently concluding that the US effort was insufficient in degree and not in kind, American military leaders felt the US should step up the air war sharply and mobilize the reserves to provide additional manpower. They urged the US president to consider invading Laos, Cambodia, and even North Vietnam to force Hanoi to cease its support for the war in the South.

Secretary McNamara felt that such a widening of the war would only result in a continuation of the present stalemate at higher levels. In 1966, Roger Fisher, a Harvard Law School professor interested in arms control, submitted a proposal to Assistant Secretary of Defense John McNaughton that would deal with infiltration down the Ho Chi Minh Trail in Laos and across the DMZ. Fisher's proposal was to block these routes "with a high tech barrier."12 Fisher's timing was perfect; McNaughton and McNamara were shopping around for a better way to reduce infiltration. In April, 1966, McNamara turned the proposal over to the Jason Division, a group formed in 1959 by the Institute for Defense Analyses and composed of about 45 of the nation's top academic scientists .

Fisher's proposal was essentially a duplication of the technological concepts used to construct the Morice Line in Algeria. It would have depended on existing technology in the form of mines, pits, barbed wire and other physical devices. The task given to the Jasons, as modified by McNaughton and McNamara, was to develop a plan for the installation of a barrier laden with state-of-the art electronic devices. In June 1966, representatives from the US military, CIA, White House, and State Department met with the Jasons at a preparatory school for girls in Wellesley, Massachusetts. The Jasons spent most of the summer developing a report on their assigned task, delivering it in person to Secretary McNamara on August 30.

The Jasons agreed with previous studies that denied the efficacy of Operation ROLLING THUNDER, noting that as of July, 1966, the US bombing of the North had "no measurable effect on Hanoi's ability to mount and support military operations in the South . . ." The Jason report went further, claiming that an expanded air campaign in the future would not prohibit Hanoi from infiltrating into the South at the current or at an increased rate. Finally, the report noted that there was "some evidence that bombings have resulted in an increased DRV [Democratic Republic of Vietnam] resolve to continue the war to an eventual victory."13 The Jason proposal for an infiltration barrier consisted of two components.

  1. An antipersonnel barrier manned by troops across the southern side of the DMZ from the South China Sea to Laos.

  2. An antivehicular barrier, primarily an aerial operation, be emplaced in and over the Laotian panhandle to interdict traffic on the Ho Chi Minh Trail.

There were certain features common to both barriers, including the employment of new technology such as remote acoustic and chemical sensors; button bomblets, which were tiny mines designed to make noise when stepped on, thereby alerting the acoustic sensors; and Gravel mines, small, cloth-covered squares designed to wound legs and feet when stepped on by enemy personnel. Gravel mines were not detectable by standard mine detectors, and the plastic pellets they fired into the body were invisible to X-rays.

The purpose of the sensors was to facilitate the acquisition of enemy "targets" for US aircraft. These target-acquisition sensors would be monitored by aircraft that would relay data to a central computer site in Thailand. The central computer would also guide attack aircraft to their targets. The air-delivered munition of choice, SADEYE/BLU-26B cluster bombs, contained one- pound bomblets in lots of 600 or more. When released, the housing broke open in such a way that the bomblets were spread across a wide area. When they impacted on the ground they exploded, dispersing steel balls embedded in the casing.

Requirements for both barriers included 240,000,000 Gravel mines; 300,000,000 button bomblets; 120,000 SADEYE cluster bombs; 19,200 acoustic sensors; 68 patrol planes; and possibly 50 aircraft for mine dispensing. The estimated total cost for these components was $800 million per year. The Jasons warned that it would be necessary to develop new technologies to stay ahead of the enemy's ability to overcome the barrier as initially proposed, thereby increasing the operating cost to close to $1 billion per year. Other associated costs included $1.6 billion for research and development and $600 million for the command center in Thailand.14 This command center would primarily support the operation in Laos.

Senior US military leaders showed little enthusiasm for the concept. Admiral U. S. Grant Sharp, the commander of US forces in the Pacific, felt the air barrier would be ineffective without ground troops to support it. General Westmoreland concurred with this view. The III Marine Amphibious Force, the senior Marine Corps command in Vietnam, disagreed with the whole barrier concept, preferring instead to employ their assets in mobile operations.15 The Jason Group recommended further study of the barrier concept, but McNamara approved implementation of their proposal without the recommended additional studies.


The US Military Command, Vietnam (MACV) modified the original Jason proposal for an antipersonnel barrier. This MACV plan in its final form called for a linear barrier, much like the Morice Line, consisting of a 600-1,000 meter wide stretch of cleared ground (or "trace") containing barbed wire, minefields, sensors, and watchtowers backed by a series of manned strong points. Behind these points would be a series of fire support bases to provide an interlocking pattern of artillery fire. This part of the system would begin at the coast of South Vietnam below the DMZ and continue westward across the coastal plain a distance of about thirty kilometers to the beginning of a more mountainous area. From this point to the Laotian border the barrier would be less comprehensive. The best routes for infiltration would be marked and blocked by minefields and barbed wire obstacles. Artillery bases located on hilltop positions would provide fire support and sites for the deployment of quick reaction forces to seek out and destroy enemy infiltrators.16

The northernmost military region of South Vietnam (Military Region I, or I Corps) was a Marine Corps area of responsibility. Marine units and Navy Seabees (engineers) began construction of the barrier in the summer of 1967, even before McNamara's public announcement of the barrier concept. Immediately after its announcement the barrier was christened "McNamara's Line."17 The final plan (III MAF Operation Plan 11-67) divided the construction into two phases. The first phase consisted of expansion of the trace, installation of a linear obstacle system, and clearing and construction of some of the strong points and base areas. Completion of the first phase was scheduled for November, 1967. The second phase, to be undertaken after the monsoon season, called for the completion of the final strong points to the west and continued obstacle construction. The completion date for this phase was July, 1968.

The McNamara Line was originally given the code name PROJECT NINE. After a partial compromise of the PROJECT NINE code name, MACV renamed the plan DYE MARKER. The Marines quickly ran into difficulty in their efforts to construct DYE MARKER. In September, 1967, the North Vietnamese launched Phase I of their "General Offensive, General Uprising" (the heart of which was the 1968 Tet Offensive). In I Corps, Phase I began with heavy North Vietnamese attacks on Marine positions along the DMZ. Besides having responsibility for the construction of the McNamara Line, the Marines had their normal tactical responsibilities in this area. It was a difficult construction environment: "At each step the Marines who were required to plow the [. . .] strip have been shot at by North Vietnamese gunners like clay pigeons in a shooting gallery."18

General Westmoreland expressed dissatisfaction with the Marines' work on the barrier project. He concluded that quality control on the project was inadequate, that DYE MARKER had not received priority commensurate with its operational importance, and that the project required more Marine command attention and better management. The Marines were ordered to do a better job. Marine feelings about DYE MARKER remained unchanged. One Marine officer expressed his opinion by stating, "With these bastards, you'd have to build the zone all the way to India and it would take the whole Marine Corps and half the Army to guard it; even then they'd probably burrow under it."19

The North Vietnamese remained uncooperative. Phase II of the North Vietnamese "General Offensive-General Uprising" took place during Tet, 1968. By January, when the McNamara Line should have become operational, it became clear that the North Vietnamese were massing around the Marine base at Khe Sanh in the northwestern corner of I Corps. On January 29, Chairman of the Joint Chiefs of Staff General Wheeler gave President Johnson a guarantee of confidence in Westmoreland's plans to defend the isolated base, a promise in writing "that the Marines would prevail at Khe Sanh."20 Westmoreland was forced by these circumstances to give top priority to Khe Sanh. All the sensors and related equipment slated to be installed along the DMZ were given instead to the defenders of Khe Sanh. Seismic and acoustic sensors were quickly dropped on likely enemy approaches by aircraft of the 7th Air Force. Almost immediately the sensors began indicating enemy activity.

In April the siege at Khe Sanh finally ended. The sensors deployed there became objects of great praise. Colonel David Lownds, the Marine commander at Khe Sanh, said, "I think the casualties would have almost doubled" without the sensors.21 One of the Jasons was less modest in his praise of sensor technology. Physicist Kenneth Case from UCSD claimed that the sensors indicated when the enemy were massing for attacks against the base, allowing the deployment of aerial and artillery bombardment which destroyed them. "That's how the Marines got out of Khe Sanh," according to Case.22

Sensor technology may have saved the Marines at Khe Sanh, but Khe Sanh effectively stopped further construction on the McNamara Line. The defenders at Khe Sanh did not face their enemy across a broad, linear front; rather, they were almost surrounded by them. The fighting there showed that sensor technology worked in 360-degree applications. There was no compelling evidence that the barrier technique would work in a linear application as envisioned by the McNamara plan.23 Commanders familiar with the success of sensor technology at Khe Sanh desired to implement the concept in a variety of operations throughout South Vietnam. As the enemy could attack from any direction, strings of sensors provided security as well as target acquisition for military installations in all areas of the country. Unlike sparsely- vegetated North Africa, the geography of Indochina made national borders impossible to seal with electronic barriers.

By the Spring of 1968 reporters noted that the infiltration barrier was far behind schedule and many military men expressed doubt that it would ever be completed. Troops along the DMZ said they had seen no evidence of any work on the line for many weeks and no indication that any efforts were underway to speed completion of the project. "I read somewhere that we were supposed to have all kinds of barbed wire and electronic devices in place along the demilitarized zone, "said a captain who had participated in several military operations in the area. "But it just is not there. If it were, I would have seen it. And I haven't seen it."24


The Ho Chi Minh Trail had been used as a communications link between north and south by the Viet Minh during their war with the French. In 1959, North Vietnam formed Group 559 to operate the trail as a means of providing transportation of material and manpower from North Vietnam to the National Liberation Front (NLF) in South Vietnam. Aerial interdiction began in 1964 by the Royal Laotian Air Force. On December 14, 1965, the US Air Force initiated Operation BARREL ROLL, the armed reconnaissance of the supply trail.

The Ho Chi Minh Trail was actually a series of trails, roads and, in some places, waterways. This supply line began in North Vietnam and entered Laos through various mountain passes. It continued south through the Laotian panhandle and penetrated South Vietnam in Military Regions I and II. Other branches of the trail continued south into Cambodia, then entered South Vietnam in Military Region III. Much of the trail passed through rough terrain with heavy jungle forests.

Early aerial interdiction attempts were designed to harass the enemy and reduce rather than completely arrest the flow of men and material. Before 1968, the war in the South was a primarily a guerrilla conflict. Five-sixths of the communist army in the South was composed of National Liberation Front units who usually mingled with the civilian population. Together with PAVN units they fought an average of one day in thirty. Their external supply needs amounted to just over thirty tons a day, and no amount of bombing could preclude this volume of material from reaching the south.25

After 1968 the nature of the fighting in Vietnam changed. The People's Liberation Armed Force (PLAF, the military arm of the NLF) was decimated by the 1967-68 "General Offensive, General Uprising" and the 1968 Tet Offensive. Although it recovered somewhat over time, it never regained its earlier strength. The burden of the fighting steadily shifter to regular PAVN units. By the time of the 1972 Easter Offensive, the PAVN accounted for 90 percent of communist military forces in the South. Militarily, the PLAF had been rendered ineffective.26 The increased logistical needs of these regular army troops meant a vastly increased amount of traffic on the Ho Chi Minh Trail.

On March 31, 1968, President Johnson announced that US aircraft would no longer bomb North Vietnam, except in the area directly north of the DMZ where enemy buildups threatened US and South Vietnamese forces. The surplus air assets of the US in Southeast Asia would be redirected from bombing North Vietnam to South Vietnam and the Ho Chi Minh Trail in Laos. The number of average daily fighter-bomber sorties in Laos increased from 25 in 1965 to over 200 in 1969.27

The McNamara Line as applied to the US aerial interdiction campaign in Laos was the continuation of existing strategy. The contribution of the McNamara Line was the addition of the latest technology to these existing efforts to make them more effective. The air portion of the barrier system was code-named MUSCLE SHOALS, and the associated technologies were christened IGLOO WHITE. The Trail was turned into a field laboratory for testing and perfecting the components of the electronic battlefield.

The flow of material on the Ho Chi Minh Trail was primarily by truck convoy.28 This flow could be reduced by both the destruction of the vehicles or by the destruction of the Trail itself. A new type of aircraft was developed for the destruction of trucks. These aircraft, known as gunships, could be equipped with night-viewing devices such as Low Light-Level Television systems and Forward Looking Infrared radiation detectors. Aimed from the front of aircraft, these devices could detect men, cooking fires, recently stopped vehicles, or foxholes inhabited by troops. Another type of thermal sensor contained a cathode ray tube that reacted to electrical ignition systems found in vehicles. Targets acquired by these devices would be destroyed by rapid-firing cannon in sizes as large as 40 mm. With firing rates of up to 6,000 rounds per minute, these gunships could operate at altitudes of 5,000 to 1,000 feet, beyond the range of small- caliber enemy anti-aircraft fire.29 Gunships equipped with sensors and automatic cannon were known as PAVE SPECTRE. The later models had additional armorplate for crew protection and increased "loiter" time. The Air Force claimed that one PAVE SPECTRE gunship destroyed 68 trucks in one hour.30

Other improvements in the methods of weapons delivery included automation of the release process. On-board computers could carry out ballistics calculations to direct the aircraft's approach run as well as the automatic release of munitions at the appropriate time. The munitions themselves had been modified to increase accuracy. Laser-guided bombs were conventional bombs fitted with a laser guidance unit. The target was illuminated by shining a beam of laser light on it. The bomb followed the beam of light to its target; moveable fins on the bomb guided it to its target. Such bombs could be released from altitudes as high as 20,000 feet and still achieved 80 percent accuracy.31 Other "smart" bombs were guided to target by radio (BULLPUP) and television cameras (WALLEYE).

As US interdiction efforts of the Trail became more intensive the enemy responded by shifting a greater volume of traffic to night hours.32 The US achieved advances in navigational precision in order to guide their aircraft in periods of poor visibility. LORAN radio beacons told a pilot his position relative to known, fixed positions on the ground. A guidance system known as PAVE PHANTOM was developed to establish a blind-bombing capacity. PAVE PHANTOM was automated to the extent that the pilot only had to input LORAN-derived data on the target position into his computer together with data about the weapons to be used. The computer would direct the aircraft over the target and release the weapon at the appropriate time. These bombing techniques were not sufficiently precise to destroy individual trucks but were able to successfully attack groups of stationary vehicles. They also could be used to blockade vulnerable trail points by causing rockslides across the roadway.33

In addition to devices that would locate targets from the air, a variety of ground sensors were developed and deployed on the Trail. These sensors were dropped by aircraft and either landed on the ground or hung from foliage. Sensors located by the enemy and tampered with would self-destruct. They were battery- operated and may have had useful lives lasting several months. Some sensors detected motion or sound. Still others were sensitive to metallic objects or to chemicals emanating from the bodies of mammals. The data produced by these sensors were transmitted via radio to receivers located at ground stations or aboard aircraft orbiting overhead. From these stations the data was relayed to a central processing site located on a military base at Nakhon Phanom, Thailand.

This Infiltration Surveillance Center (ISC) was the heart of the IGLOO WHITE system. After the data was sorted by computer it was passed to target analysts who would send their assessments to the strike aircraft and direct them to their targets. The ISC computers contained extensive and precise mapping of the Ho Chi Minh Trail system. The normal time between target acquisition by sensors and munitions delivery by aircraft was less than five minutes and could be as little as two minutes.34 Computers would predict the expected path and speed of truck convoys by sensor read-out. Aircraft were vectored to a particular point and their munitions were automatically released at a time that would coincide with the arrival of the truck convoy in the killing zone. This interdiction system had all-weather capability, and no ground forces were needed.

Project IGLOO WHITE was in operation from 1968 until the end of 1972. US Air Force figures indicate that the bombing campaign destroyed a great number of trucks: 5,500 in 1968; 6,000 in 1969; 12,000 in 1970; and 12,000 in 1971, the last full year of its operation. Official estimates held that each truck carried 10,000 pounds of military supplies. In 1971 only 20 percent of the supplies that entered the Trail system made it to their destination. According to an Agence France reporter who viewed the scene, physical damage to the Trail area was tremendous:

On each side of the road there are heaps of scrap metal, pieces of aircraft, the containers of antipersonnel bombs, empty munitions, 37-mm. [PAVN] cannon shells, detonated antipersonnel mines . . . At certain points, it is impossible to walk on the sides of the roads. You sink up to your knees in an impalpable dust, the earth having become dust under the impact of the bombs and incendiary weapons . . . When the monsoon comes, that dust turns into mud and slides onto the roads . . . nothing lives in this dust, not even crickets. Only man is residing in it.35
IGLOO WHITE began to cease operations in December, 1972. Reasons given were because the prospects for a cease-fire seemed promising and because operational costs were high. Further, the PAVN had shelled Saigon in December, 1971. President Nixon felt this attack violated the terms of the 1968 bombing halt agreement. Nixon's response to this breach was to resume the bombing of North Vietnam with Operation DEEP ALPHA, striking targets up to the 20th parallel. As the US Air Force was concentrating on achieving interdiction while war material was still in North Vietnam, there was less reason to bomb in Laos. Enemy traffic on the Trail dwindled considerably.36 The last US bombing raid on the Ho Chi Minh Trail was a B-52 strike in April, 1973.37


By March, 1972, almost all the US ground combat forces had left Vietnam. There was only one remaining ground surveillance station in I Corps. The sensor technology was still classified by the Americans and would not be turned over to the South Vietnamese Army. The sensor read-out bunker of Advisory Team 155 near the Quang Tri Combat Base, scheduled for deactivation in May, had been picking up enemy movement for weeks. On March 28, the US advisors to the South Vietnamese military began getting numerous solid readings during daylight hours, something that had not happened since the US withdrawal. Two days later the North Vietnamese Army launched its largest offensive of the entire war, invading across the DMZ with three infantry divisions supported by armor and artillery.38 The remnants of McNamara's Line would not stop them.

Aerial interdiction operations executed in conjunction with ground forces can achieve great tactical success. Aircraft operating independently are able to cause great destruction but with little operational reward. In early 1944, Allied air planners tried to employ aerial interdiction alone to cut off the flow of German troops and supplies to the Gustav Line in Italy, thereby forcing the Germans to withdraw. With no role for Allied ground forces it soon became clear that this operation would not succeed.

During the Korean War, air power proponents had to relearn the lessons of the limits of aerial interdiction. By 1951, the front in Korea had become stabilized. US air planners initiated a massive aerial interdiction campaign designed to cut off the source of supply for the North Korean Army and force them to withdraw. The Korean communists were only inconvenienced and their positions held. Aerial interdiction without ground maneuver again proved irrelevant after Chinese troops invaded Korea.39 Even though the span of time between World War II and Vietnam was relatively brief, US air planners proved unable to transfer these lessons to Indochina.

The antipersonnel barrier across the DMZ was never constructed as planned. Much of the proposed barrier was within range of enemy artillery situated just north of the DMZ, and the entire area was the object of frequent probes by the PAVN. US military forces were never of sufficient strength to construct and man the barrier adequately while fighting the enemy at the same time. Had the barrier been built in the early years of US involvement in the war, it would have faced much less opposition to its implementation. However, until the North Vietnamese escalated the fighting to high levels in the mid-1960s, the perceived need for a barrier was insufficient to order its construction.

Had an effective barrier been constructed, the PAVN would undoubtedly have chosen to go around it, an option that was not available to FLN guerrillas while operating as large units in Algeria. Communist soldiers who were needed in Military Regions II, III, and IV clearly would have had an easier time outflanking the barrier via the Ho Chi Minh Trail than fighting their way through hundreds of thousands of US and ARVN soldiers located in Military Region I (MR I). Fighting that did occur in MR I was usually initiated by the communists for the purpose of tying up the military assets of the Americans and South Vietnamese.

Unlike the antipersonnel barrier, the antivehicular barrier across the Laotian panhandle was a thorough implementation of the Jason plan. It was successful in destroying a great quantity of military supplies. Undoubtedly many enemy soldiers were killed as well; over one million tons of bombs were dropped on the Trail by the US and its allies during the period 1965 until 1971.40 But the Trail network was too extensive to be shut down by any amount of bombing; the enemy eventually disclosed that the network extended over thirteen thousand kilometers. The communists were largely successful in controlling the level of fighting during the Vietnam War. When supplies were inadequate to support military activity at high levels, the enemy reduced its operations until sufficient material became available to them. Between 1966 and 1971 the Trail was used to infiltrate 630,000 troops, 100,000 tons of food, 400,000 weapons, and 50,000 tons of ammunition into South Vietnam.41 The harder the US tried to interdict the trail the more sophisticated it became. In the early days most infiltration on the trail was by human porters walking on narrow paths. By 1972 it contained paved roads capable of handling armored vehicles and a petroleum pipeline. CIA Director Richard Helms offered the following comment on the effectiveness of the US interdiction program in Laos:

"Look: before the bombing they used to send three men south to get two in place. Now they have to send five. We're willing to lose planes, they're willing to pay in manpower. So it doesn't make a particle of difference. There are more dead bodies. But in terms of net result, it doesn't make a damned bit of difference."42
Unlike the McNanara Line in Vietnam, the Morice Line in Algeria was a military success. The nationalist army was effectively isolated from external support. In the first three years of fighting the ALN (the military forces of the FLN) lost over 30,000 killed and 13,000 captured. "This meant . . . the ALN had been almost wiped out at once."43 France was strong militarily in Algeria but weak politically at home. For both the French and the Americans, continued fighting caused a reduction in domestic support for their military endeavors abroad. Both nations experienced dissatisfaction within their armed forces as to the conduct of the wars. Both nations underwent constitutional crises related to the continuation of the fighting.

Eventually France concluded its efforts to main the colonial status of Algeria were not worth the price. It was a similar evolution of circumstances that denied the US military success in Vietnam, its overwhelming military and technological superiority notwithstanding.


1 New York Times, September 8, 1967, 6, and New York Times, September 9, 1967, 4.

2 See Arther Ferrill, "The Secod Oldest Profession," (MHQ: The Quarterly Journal of Military History, Vol. 3, No. 1, Autumn, 1990, pp. 24-29) for a discussion of organized warfare during the Neolithic Age. Ferrill notes that at Jericho, one of the oldest human settlements ever excavated, defensive walls were constructed before it became a settled agricultural community.

3 Joseph Buttinger, The Smaller Dragon (New York: Praeger, 1958), 168.

4 John Prados and Ray W. Stubbe, Valley of Decision (Boston, MA: Houghton Mifflin, 1991), 141.

5 John Talbott, The War Without a Name (New York: Alfred A. Knopf, 1980), 184. This description of the Morice Line is from Talbott and from Alistar Horne, A Savage War of Peace (New York: Viking Press, 1977), 264-266.

6 Prados, Valley of Decision, 10-11.

7 Ibid., 11.

8 General William Westmoreland, A Soldier Reports (New York: Doubleday, 1976), 147-148.

9 George C. Herring, America's Longest War (New York: Knopf, 1979), 128.

10 Westmoreland, A Soldier Reports, 154 and 193.

11 The Pentagon Papers (New York Times Edition) (New York: Bantam Books, 1971), 523.

12 Ann Finkbeiner, "Jason: Can a Cold Warrior Find Work?" Science, 29 November 1991: 1285.

13 Paul Dickson, The Electronic Battlefield (Bloomington: Indiana University Press, 1976), 24-25.

14 For descriptions of the components of the barrier in Vietnam, see Dickson, The Electronic Battlefield, 25-28; The Pentagon Papers, 507-509, and Prados, Valley of Decision, 141-142.

15 For a discussion of military opposition to the barrier concept, see Major Gary L. Telfer, Lieutenant Colonel Lane Rogers, and V. Keith Fleming, Jr., U.S. Marines in Vietnam, 1967 (Washington, D.C.: Headquarters and Museums Division, U.S. Marine Corps, 1984), 86-87.

16 For a description of the manned positions that were constructed by the Marines under this barrier concept, see Otto J. Lehrack, No Shining Armor (Lawrence, Kansas: University Press of Kansas, 1992), 181-183.

17 According to U.S. News & World Report (January 1, 1968, p. 24) this name was given to the barrier by anonymous soldiers in the field on the same day that McNamara announced the barrier would be constructed.

18 William R. Corson, The Betrayal (New York: Norton, 1968), 78.

19 Telfer, U.S. Marines in Vietnam, 1967, 94.

20 Robert Pisor, The End of the Line (New York: Ballentine Books, 1982), 118.

21 United States Congress. Senate Armed Services Committee. Permanent Investigations Subcommittee. Hearings: Investigation into Electronic Battlefield Program. 91st Congress, 2nd Session (Washington, D.C.: Government Printing Office, 1971), 95. (Hereafter Electronic Battlefield Program Hearings).

22 Finkbeiner, "Jason: Can a Cold Warrior Find Work?", 1286.

23 An example of the non-linear nature of the battlefield at Khe Sanh is illustrated by the deployment of PAVN troops. One PAVN division was located north and northwest of the base. Another was located to the south and southwest. The largest ground attack at Khe Sanh was by PAVN soldiers who bypassed the DMZ and attacked from the east. See Captain Moyers S. Shore, The Battle for Khe Sanh, (Washington, D.C.: History and Museums Division, Headquarters, U. S. Marine Corps, 1969), 29 and 123-124.

24 New York Times, March 25, 1968, p. 1.

25 Mark Clodfelter, The Limits of Air Power (New York: The Free Press, 1989), 205.

26 Douglas Pike, PAVN: People's Army of Vietnam, (New York: Da Capo Press, 1986), 49.

27 Raphael Littauer and Norman Uphoff, eds., The Air War in Indochina, (Boston: Beacon Press, 1971), 70.

28 The majority of the trucks used on the Trail were Soviet Zil 157 six-wheel drive vehicles. Capacity was 5,500 to 9,900 poundss of cargo at speeds up to 41 mph over Laotian roads. Electronic Battlefield Program Hearings, 160.

29 Aviation Week and Space Technology, May 10, 1971, 76.

30 Dickson, The Electronic Battlefield, 86.

31 Aviation Week and Space Technology, June 22, 1970, 167.

32 According to testimony by Major General Carlos Talbott, USAF Director of Operations, 98 percent of enemy traffic on the Trail was conducted at night. Electronic Battlefield Program Hearings, 107

. 33 New York Times, April 11, 1971, 4.

34 Dickson, The Electronic Battlefield, 87.

35 Quoted in Dickinson, The Electronic Battlefield, 90-91.

36 New York Times, October 23, 1972, 2.

37 Christopher Robbins, The Ravens, (New York: Crown Publishers, 1987), 326.

38 Colonel G. H. Turley, The Easter Offensive (New York: Warner Books, 1985), 50-53.

39 Robert R. Leonhard, The Art of Maneuver, (Novato, CA: Presidio, 1991), 161-162.

40 Littauer, The Air War in Indochina, 281.

41 Robbins, The Ravens, 289-290.

42 Ibid.

43 Edgar O'Ballance, The Algerian Insurrection, 1954-1962, (Hamden, CT.: Archon Books, 1967), 92.

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