Project Dye Marker

Project Dye Marker was a cover name for an electronic anti-infiltration barrier system with a strong point/obstacle component. It was partially constructed by the American forces in 1967-1968 in South Vietnam along the eastern portion of the demilitarized zone. Some stretches of the defensive line were manned and equipped with the bunkers, outposts, reinforcing and fire support bases, surrounded by concertina wire. Other parts were under constant radar, motion and acoustic surveillance, and secured by trip wires, mine fields, and barbed-wire entanglements. Anti-infiltration barrier was a vital part of a strategic program unofficially referred to as McNamara Line, (after the Secretary of Defence Robert McNamara), running across South Vietnam deep into Laos. McNamara Line was a grand scale, multimillion project, and was nicknamed in the media as Great Wall of Vietnam, McNamara's Wall, Electric Fence, and Alarm Belt.

Dye Marker
The Dye Marker defensive line, previously called Practice Nine, stretched along the demilitarized zone starting from the South China Sea, and had a total length of 76 kilometers (47 miles). Construction was announced on September 7, 1967, and was carried out by the 3rd Marine Division. The plan called for a barbed wire fence with watch towers, which was presented to the public as a barrier. First, the 11th Engineers started to work on bulldozing the Trace, a path 600 meter wide and 11 kilometers long that was stripped of trees, brush and villages if needed. The backbone of the strong-point system were fortified bases Alpha 2 at Gio Linh on the east, Alpha 4 at Con Thien on the west, and Alpha 3 in between.

The strong-point part of the anti-infiltration system in Quang Tri Province, Vietnam was also reinforced with electronic sensors and gravel mines. It intended to curb the flow of North Vietnamese troops and supplies through the demilitarized zone during the decisive years of the Vietnam War. 7,578 American marines have been deployed in support of Dye Marker strong point/obstacle system by 1 November 1967. In addition, 4,080 American troops have been involved in the air-supported anti-infiltration part of Dye Marker. The strategic meaning of the Dye Marker, as well as a whole McNamara Line, which ended in Laos, was to stop infiltration of South Vietnam by the NVA forces. This would have allowed McNamara to scale back the American bombing of North Vietnam and start negotiations with Hanoi.

Criticism
The defensive barrier system was criticized at the time of its inception for keeping American troops in static positions while facing mobile enemy forces.