Khe Sanh 1968: Igloo White Sensors, a Nuclear Option and Operation Charlie

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Khe Sanh, in Quang Tri province just seven miles from Laos on Route 9, began in 1962 as a small Special Forces outpost watching the border. General William Westmoreland built it into a base for future operations against the Ho Chi Minh Trail over the objections of Marine General Lewis Walt, who wanted to focus on protecting the populated coast. In late 1967 North Vietnamese regiments fought costly set-piece border battles such as the 22-day fight at Dak To, and Westmoreland welcomed the chance to use American firepower away from the cities. The siege began at 1:30 a.m. on January 21, 1968, when an early shell hit the main ammunition dump, setting off a tear gas cache, killing 14 Marines and wounding 43. Days later the Tet Offensive struck more than 100 cities and outposts across South Vietnam.

Operation Niagara poured bombs on the hills, aimed with help from Igloo White, a network of acoustic and seismic sensors dropped from aircraft whose signals were relayed to computers in Thailand. North Vietnamese troops answered by digging trenches by hand to within 25 meters of the perimeter, as at Dien Bien Phu in 1954. On February 7, Soviet-built PT-76 tanks overran the Lang Vei Special Forces camp, the first North Vietnamese use of armor in South Vietnam, and Colonel David Lownds refused to send a relief force until Westmoreland intervened. Westmoreland also began planning for possible tactical nuclear weapons, which McNamara and Johnson rejected. Operation Pegasus relieved the base in April after 77 days, then on June 19 Operation Charlie ordered it destroyed and abandoned, leaving historians to argue over who was diverting whom.

• An average day brought 350 tactical fighter bombers and 60 B-52s over Khe Sanh, and more than 100,000 tons of bombs fell in the first three months.
• C-130s delivered up to 185 tons of supplies a day using LAPES, pulling pallets out by parachute while flying about five feet above the runway.
• Lang Vei's survivors, including Green Berets and civilian refugees, were kept outside the Khe Sanh wire overnight over fears of infiltrating sappers.
• Lyndon Johnson kept a terrain model of the base in the White House and had the Joint Chiefs sign a pledge that it would not fall.
• A 1974 North Vietnamese study describes an option play: take the base if possible, and if not, tie down tens of thousands of American troops.