By late January 1968, American intelligence sources had detected 20,000 or more NVA soldiers in the vicinity of Khe Sanh. American tactics were to allow the enemy to surround the 26th Marine Regiment (Reinforced) at Khe Sanh, to mass their forces, reveal troop formations and logistic routes, establish storage and assembly areas, and prepare siege works. The result would be the most spectacular targets of the Vietnam War for American firepower.

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General William C. Westmoreland, commander of U.S. forces in Vietnam, chose the code name ‘Operation Niagara’ for the coordination of available firepower at Khe Sanh. According to Westmoreland, the name Niagara invoked an appropriate image of cascading shells and bombs. Niagara would be composed of two elements. Niagara I was the comprehensive intelligence-gathering effort to pinpoint the available targets, and Niagara II was the coordinated shelling and bombing of these targets with all available air and artillery assets.

The effectiveness of the firepower available to the Marines at Khe Sanh was heavily dependent on target selection–a responsibility of the intelligence section (S-2) of the 26th Marine Regiment Headquarters Company. S-2 knew the siege strategy employed by the NVA at Dien Bien Phu in 1954 and Con Thien in 1967, and it could predict the enemy’s actions at Khe Sanh.

Various sources were utilized to keep track of enemy activity around the Khe Sanh plateau. Sources outside the immediate battlefield included intelligence reports from MACV in Saigon, III Marine Amphibious Force (III MAF) headquarters in Da Nang, as well as the headquarters of the 3rd Marine Division at Phu Bai.

Intelligence was generated locally in many ways. Hundreds of acoustic and seismic sensors were seeded around the combat base. This comprehensive sensor system cost approximately $1 billion and was credited with reducing Marine deaths during the fighting by 50 percent. By Marine estimates, the sensor system provided 40 percent of the raw intelligence at Khe Sanh. Ground and aerial observers supplied visual evidence of enemy activity, as did photoreconnaissance. Analysis of incoming rocket, mortar and artillery craters determined the likely source of the attacks. Shell/flash reports, infrared imagery and analysis of intercepted enemy communications were also used to identify potential enemy targets.

Marine reconnaissance patrols, Army Special Forces, CIA personnel, and the MACV-SOG all provided input to the 26th Marines S-2. The CIA Joint Technical Advisory Detachment and SOG obtained their information from casual encounters with villagers; from regular paid agents, including Rhade and Bru Montagnards; and from locals who wanted to be agents of the U.S. intelligence community around Khe Sanh. Likely or confirmed targets were then pummeled by the available firepower, while the base Fire Support Coordinating Center (FSCC) coordinated the array of supporting arms.

After making the trip down the Ho Chi Minh Trail through Laos, the NVA established various forward logistic bases within a few thousand meters of the combat base. At night the Communists dug shallow trenches from their supply points toward the U.S. positions. American intelligence noticed this trenching system around February 23, 1968. Once the system had been constructed close to the base, secondary trench lines branched off and paralleled the Marine perimeter. These close-in, secondary trenches were dug for the purpose of launching ground attacks against the base.

Initial FSCC fire tactics were to saturate infiltration routes into the area around the combat base with artillery fire and airstrikes. This slowed down NVA trenching efforts but could not stop them completely. From a logistic standpoint, it was impossible to sufficiently saturate the trenching systems with massed artillery fire, so the FSCC altered its tactics. The NVA was permitted to dig trenches close to the base–then it was easier to pinpoint them.

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