8 March 1967 – Construction began on the “McNamara Line”, an operational strategy aimed to prevent infiltration of South Vietnam by NVA forces from North Vietnam and Laos. “The McNamara Line was first given the code name “Project Nine.” MACV, U.S. Military Command, Vietnam, then changed the name of the plan to “Dye Marker,” following a compromise of the classified Project Nine sobriquet.” (1)
“Physically, the McNamara Line ran across South Vietnam from the South China Sea to the Laotian border along the Vietnamese Demilitarized Zone (DMZ). 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. It was planned as a physical barrier supported by electronic sensors and extensive minefields.
In September of 1967, “the North Vietnamese began Phase I of their “General Offensive, General Uprising” campaign by attacking marine positions along the DMZ. That made it especially difficult to advance the McNamara Line’s construction.
In mid-1968, the physical barrier concept was pushed aside after the North Vietnamese overran the Lang Vei Special Forces camp and besieged Khe Sanh. The barrier concept was reduced to an aerial, sensor-based electronic interdiction program that was to be conducted in Laos. (2)
Sources: (1) u-s-history.com; (2) Wikipedia