McNamara Line The McNamara Line was an unofficial name for a defensive project initiated by the United States between 1966 and 1968 during the Vietnam War to prevent infiltration of South Vietnam by NVA forces from North Vietnam and Laos . The McNamara Line ran across South Vietnam from the South China Sea to the Laotian border along the Vietnamese Demilitarized Zone ( DMZ ) . It included fortified field segments with Khe Sanh as linchpin , along with open spaces , where road and trails were guarded by the high - tech acoustic and heat - detecting sensors on the ground and interdicted from the air . A sophisticated electronic surveillance was backed with gravel mines and troops at choke points . Named the barrier system by Robert McNamara , it was one of the key elements , along with gradual aerial bombing , of his war strategy in Vietnam . Barrier concept . Various schemes had been proposed in the years before 1965 for a defensive line on the northern border of South Vietnam and in southeast Laos . These schemes had generally been rejected because of their requirements for large amounts of military personnel to be deployed in static positions and because any barrier in Laos would encourage the Vietnamese to deploy their forces deeper into Laotian territory . In December 1965 , Robert McNamara met twice with Carl Kaysen , a former Kennedy - era National Security Council staff member . Kaysen proposed an electronic barrier to limit infiltration from North Vietnam . McNamara embraced the idea and asked Kaysen to create a proposal . Starting in January , John McNaughton and a group in Cambridge , Massachusetts , including Kaysen and Roger Fisher created the proposal which was submitted to McNamara in March 1966 , who then passed it to the Joint Chiefs of Staff ( JCS ) for comment . The JCS response was that the proposal would still require an infeasible number of troops to be stationed along the barrier and would present difficult construction / logistical problems . Also in late 1965 or early 1966 , Jerry Wiesner and George Kistiakowsky persuaded McNamara to support a summer study program in Cambridge for the group of 47 prominent scientists and academics that made up the JASON advisory division of the Institute for Defense Analysis . The subject of the study was to find alternatives to the majorly unsuccessful gradual airial bombing campaign in North Vietnam advocated by McNamara . As Kaysen and the others involved in the Cambridge group were all members of JASON scientific advisory group , the anti - infiltration barrier ideas were included in the JASON agenda . JASON study group . The JASON study group meetings took place June 16 – 25 , 1966 at Dana Hall in Wellesley , Massachusetts . The buildings were guarded day and night and attendees were given top secret security clearances . After the summer meetings , a report was produced over the course of July and August . The JASON report of August 1966 called the bombing campaign against North Vietnam a failure saying that it had " no measurable direct effect on Hanoi ' s ability to mount and support military operations in the South " . Instead , advisors proposed as an alternative two defensive barriers . The first barrier would run from the coast some distance inland along the demilitarized zone and would seek to block the NVA infiltration through conventional means . The second barrier would run from the remote western areas of the border into Laos and would be a barrier of air interdiction , mine fields and electronic detection requiring minimal troops . While the JCS report had estimated the construction of a barrier would take up to four years , the JASON report suggested the barrier could be in place with available resources within a year . That was important to McNamara since he hoped that by cutting the logistics lines between the North and the South he would have been able to press Hanoi into negotiations . Decision - making . In September 1966 , McNamara presented the JASON group report to the Joint Chiefs . It had split on the proposal with the service chiefs being against it , and general Earle Wheeler , a Chairman of JCS , being in support . The JCS then handed the report off to the Commander - in - Chief , Pacific ( CINCPAC ) admiral Sharp , who wrote back that the barrier idea was impractical from a manpower and construction point of view . General William Westmoreland , who was commanding officer in Vietnam , was apprehensive of the idea and reportedly was even afraid that the barrier would go into history as " Westmoreland ' s Folly " . Despite all disagreements , on September 15 , 1966 , without waiting for the final judgment of the JCS , the U . S . Secretary of Defense Robert McNamara ordered that the proposal be implemented . General Alfred Starbird , director of the Defense Communications Agency , was appointed head of Task Force 728 , which was to implement the project . Two days later , the JCS reported back favorably on the already - decided plan . Starbird had to complete the barrier by September 1967 . In November 1966 , McNamara officially recommended the barrier system to President Johnston for implementation . The construction budget was estimated as $ 1 . 5 billion , and $ 740 million was allocated for the annual operating costs . " The Practice Nine " was adopted as the barrier project internal communication code name . Chronology . On January 13 , 1967 , President Johnson authorized the construction , and it was assigned the highest national priority . Cover name change . In June 1967 , an existence of " Practice Nine " was leaked to the press . The project was then renamed as " Illinois City " and in September it was called " Project Dye Marker " . Further , it was also referred to as " SPOS " ( Strong - point - obstacle - system ) , with two different components , " Dump Truck " ( anti - vehicle ) and " Mud River " ( anti - personnel ) , which were collectively referred to as " Muscle Shoals " . 1967 . USMC Engineers in early 1967 were already ordered to bulldoze a strip to at least 500 meters wide from Gio Linh westward to Con Thien . This became known by the Marines as " The Trace " . Construction began in the summer 1967 . 1968 . At the beginning of 1968 , the western end of the fortified part of the barrier still under construction stretching from Khe Sanh through the special forces camp at Lang Vei was attacked by the multiple North Vietnamese troops . The special forces camp at Lang Vei was overrun and Khe Sanh was placed under siege . The Battle of Khe Sanh lasted for seventy seven days . In July 1968 , General Abrams newly appointed as US commander in South Vietnam ordered Khe Sanh and the surrounding area to be abandoned . The base was dismantled and all the infrastructure along Route 9 toward Laos including roads and bridges was systematically destroyed . On 29 October 1968 , construction work ceased on the physical barrier to the east along the demilitarized zone on South Vietnam ' s side . The physical infrastructure created for the barrier was converted into a series of strong - points and support bases for the new strategy of mobile operations . This marked the end of the " McNamara Line " as an operational strategy . Significance of the barrier strategy . In his memoirs , Robert McNamara insisted that the barrier , or the " system " , as he chose to call it , was able to cut to a degree an infiltration rate of the NVA to South Vietnam . However , constructed segments turned to be inefficient in stopping the NVA despite being costly to build and maintain . In March 1969 , most of the strong points of the barrier manned by troops were abandoned . A system of sensors to provide surveillance of the truck routes from Laos was successful , but its counterpart for the foot trails was never deployed . Many special munitions ordered for the barrier turned to be ineffective or simply failed . In 1969 , Defense Secretary Melvin R . Laird testified in Congress that goals set for the anti - infiltration barrier were not met despite it high cost . An official account of the 1965 - 1969 , published in the " Secretaries of Defense Historical Series " , stated that the interdiction significance of the barrier remains contentious . At the same time , it reserved harsh words for McNamara ' s inability to listen and called the so - called McNamara Line :