In September 1967, U.S. Secretary of Defense Robert S. McNamara announced a plan for the construction of an electronic anti-infiltration barrier south of the DMZ in Vietnam. The stated purpose of the barrier was to u0093sound the alarmu0094 when North Korean troops attempted to enter the protected area. Once detected, U.S. forces and its allies would respond with air strikes and artillery bombardment.
What a concept
Artificial barriers predate even the cultivation of plants. The Great Wall of China and Hadrianu0092s Wall in Great Britain were erected to block the tide of invading barbarian forces. Even Vietnam itself was home to two huge walls built by the Nguyen to separate themselves from the northern Trinh armies in the early 1600s.
The French considered constructing a barrier at the narrow part of Vietnam. After their defeat at Dien Bien Phu in 1954, the plan became irrelevant. The French did, however, construct a meaningful barrier in Algeria, called the Morice Line, in 1957. The Maginot Line was likewise constructed by the French prior to World War II.
The barrier concept in Vietnam was considered as early as 1958 by American advisory personnel. Another proposal was put forth in 1961 to create a u0093cordon sanitaire,u0094 or quarantine line, along the South Vietnam-Laotian border to prevent infiltration by the North Vietnamese. The Southeast Asia Treaty Organization (SEATO) proposed a similar concept, manned by international forces, along the DMZ and the Laotian panhandle, in the same year. General William Westmoreland also backed a similar plan in 1964.
Those barrier proposals were put on the back burner because it was thought, by officials in Washington, that heavy bombing initiated by Operation Rolling Thunder would slow the infiltration.
According to The Pentagon Papers, bombing sorties numbered 55,000 in 1965 and increased to 148,000 in 1966. Bomb tonnage rose from 33,000 in 1965 to 128,000 and the number of aircraft lost rose from 171 to 318 with estimated costs totaling $1.2 billion in 1966.
As the realization dawned that the bombing policy was not having its desired affect, McNamara began to seek other options.
A plan was devised by Harvard Law School professor Roger Fisher to install a barrier of state-of-the-art electronic devices along the DMZ and the Ho Chi Minh Trail. The idea was turned over to the Jasons, an elite group of about 45 of the nationu0092s leading academic scientists. They reached the same conclusion on the bombing issue and expanded the infiltration barrier concept to include two components:
An antipersonnel barrier, manned by military personnel, spanning south of the DMZ from Laos to the South China Sea, a distance of about 160 miles. The antipersonnel barrier was to comprise minefields, ditches, barbed wire, and defoliated strips with military strongholds at specified, geographically advantageous positions.
An antivehicular barrier to interdict traffic on the Ho Chi Minh Trail. The barrier was to consist of numerous sensoring devices of various styles and applications, and monitored in Nakhon Phanom, Thailand.
Of operating acronyms and code names
The McNamara Line was first given the code name u0093Project Nine.u0094 MACV, U.S. Military Command, Vietnam, then changed the name of the plan to u0093Dye Marker,u0094 following a compromise of the classified Project Nine sobriquet.
At that time, September 1967, the North Vietnamese began Phase I of their u0093General Offensive, General Uprisingu0094 campaign by attacking marine positions along the DMZ. That made it especially difficult to advance the McNamara Line`s construction.
As January 1968 came and went, NVA troops were massed for an all-out attack on the Marine base at Khe Sanh as part of the Tet Offensive. Sensors and hardware had to be diverted from other parts of the DMZ to Khe Sanh. After that siege ended in April, construction on the McNamara Line was abandoned.
Interdicting the Ho Chi Minh Trail
As bombing shifted in March 1968 from North Vietnam to the Ho Chi Minh Trail in Laos, the antivehicular barrier helped to increase the effectiveness of fighter-bomber sorties. The air portion of the mission to place the sensors along the trail was code-named u0093Muscle Shoals,u0094 while the electronic interpretive technologies held the tag of u0093Igloo White.u0094
The sensors were about 20,000 in all, either seismic or acoustic, some half-embedded in the ground, others dropped by parachute so they would hang in the trees. They came in three main types:
The u0093Acoubuoy,u0094 36 inches long and 26 pounds, were camouflaged and floated down by parachute;
the u0093Spikebuoy,u0094 66 inches long and 40 pounds, stuck in the ground like a lawn dart with the antenna camouflaged to resemble weeds;
and the ADSID (Air-Delivered Seismic Intrusion Detector), resembling a Spikebouy but smaller at 31 inches and 25 pounds u0097 the most widely used sensor.
Other sensors included a u0093people sniffer,u0094 designed to sense sweat and urine. The newly installed u0093Black Crowu0094 detection system could sense truck engine emissions from 10 miles away.
As Igloo White interpreted signals from the sensors, they sent out directives to guide newly developed gunships to their targets. The code name for those AC-130 gunships was u0093Pave Spectre.u0094 They carried 40mm cannons capable of firing 6,000 rounds per minute.
Igloo White was disbanded in 1972 because of high operational costs, and military officials thought a cease-fire was imminent.
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