Physically, the McNamara Line ran across South Vietnam from Cửa Việt port to Route 9 and to the Laotian border along the Vietnamese Demilitarized Zone (DMZ) till Mường Phìn, Laos.
[1] The eastern part included fortified field segments, with Khe Sanh as linchpin, along with stretches where roads and trails were guarded by high-tech acoustic and heat-detecting sensors on the ground and interdicted from the air.
Named the barrier system by Robert McNamara (United States Secretary of Defense from 1961 to 1968), it was one of the key elements, along with gradual aerial bombing, of his war strategy in Vietnam.
Starting in January, John McNaughton and a group of scientists 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 comments.
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.
[5] 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".
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.
An effective anti-infiltration barrier, running across South Vietnam deep into Laos, was a grand vision of the US Secretary of Defence Robert McNamara, who feared that escalation of bombing can bring greater Chinese involvement,[9] and a vital component of his operational strategy.
First, the 11th Engineers started to work on bulldozing the so-called Trace, a path 600 meter wide and 11 kilometers long that was stripped of trees, brush and villages if needed.
[15]: 4 The Dye Marker defensive line project stretched along the demilitarized zone starting from the South China Sea, and had a total length of 76 kilometers (47 miles).
[8][16] The plans that were leaked to the media called for an inexpensive barbed wire fence with watch towers, and they were presented to the public as a trivial measure, while the electronic part was highly classified.
[12] At the beginning of 1968, the western end of the barrier region stretching from Khe Sanh through the special forces camp at Lang Vei was attacked by the multiple North Vietnamese troops.
[17] 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.
[3]: 509 An official account of the Vietnam War, published in the Secretaries of Defense Historical Series, stated that the interdiction significance of the barrier remained contentious.
[3] The defensive barrier system was also criticized at the time of its inception for keeping American troops in static positions while facing mobile enemy forces.
[15] After the Tet Offensive, the criticism intensified, and Senator Stuart Symington (D-Missouri) called the barrier a "billion dollar Maginot line concept".