The sensor system quickly proved its worth. During the night of February 3-4, sensors detected up to 2,000 NVA soldiers in the vicinity of Marine hill outposts northwest of the combat base. Defensive artillery fires were ordered against them, and sensors reported hearing men screaming in panic and the sounds of troops fleeing their assembly areas. The NVA units were completely destroyed in their assembly areas and the intended attack was effectively broken up. This is one of the earliest examples in warfare of a ground attack entirely thwarted by using remote sensor data.

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With crater analysis, it was possible to confirm the location of enemy batteries, assist in counterbattery fires and detect new types of enemy weapons–new calibers or new munitions. The flight direction of a projectile could be determined with reasonable accuracy from its crater, ricochet furrow or, in the case of dud rounds, soil tunnel.

The particular characteristics of the soil at Khe Sanh often yielded valuable information through crater analysis. A stick placed in the soil tunnel made by a dud round would point in the direction of origin, and the angle of the stick would indicate the angle of fall. By measuring this angle and using the firing tables of enemy weapons, counterfire personnel could compute the range of the enemy weapon. Shelled areas were inspected as soon as possible after a shelling.

Staff Sergeant Bossiz Harris, the acting gunnery sergeant of the mortar battery, 1st Battalion, 13th Marines, conducted crater analysis during incoming fire, which allowed the battalion’s Fire Direction Center (FDC) to direct prompt return fire. Rapid and accurate counterbattery fire could force the enemy artillerymen to seek cover and could destroy NVA guns and gun crews.

To minimize the reaction time of the Marine and Army artillerymen at Khe Sanh, Colonel Lownds, the base commander, periodically entered the regimental FSCC bunker, indicated a spot on the wall map and directed the senior artillery officer to hit the marked spot. The coordinates were sent to the FDC, computed and sent to the appropriate gun crew, which adjusted its tubes. This aiming process usually took less than 40 seconds before a round was on its way. During the battle at Khe Sanh, the 1st Battalion, 13th Marine, guns fired 158,891 mixed artillery rounds in direct support of the 26th Marines.

Acquiring data on enemy troop locations was one thing, but correctly interpreting it was quite another. On the first day of the 1968 Tet Offensive, intelligence analysts on the MACV staff received a set of infrared imagery photos. The photos were interpreted as indicating NVA troop movements away from the combat base, while sensor readout data showed these troops were closing in on the base in preparation for a massive attack. In actuality, no enemy ground attacks were launched around Khe Sanh during this period.

Shortly after the beginning of the Tet Offensive, aerial reconnaissance and communications intelligence indicated a major target in the Khe Sanh Tactical Area of Responsibility (TAOR). Photo analysts spotted a bank of radio antennas at a limestone cave complex in the DMZ northwest of Khe Sanh, and radio signals emanating from it showed the caves to be a major enemy headquarters. There was speculation that NVA General Vo Nguyen Giap himself was supervising the battlefield from the caves. Repeated Boeing B-52 attacks by the U.S. Seventh Air Force knocked the enemy radio system off the air temporarily and even managed to seal the cave entrance with rocks and other debris. In spite of these attacks, the cave headquarters remained in operation for several weeks.

One Marine spotter on Hill 881 South, Lance Cpl. Molimao Niuatoa, had especially sharp vision. Niuatoa was scanning the landscape with a pair of 20-power naval binoculars when he saw the muzzle flash of an NVA artillery piece 12,000 to 13,000 meters from his position. Because the gun position was beyond the range of Marine artillery, it could only be taken out by airstrikes, and an observation aircraft was directed toward the position. Since the observer did not know the exact location of the gun, he fired a 2.75-inch smoke rocket into its general vicinity. A Marine Douglas A-4 Skyhawk jet dropped a 500-pound bomb on the marking rocket. Niuatoa observed how far the billowing bomb smoke was from the artillery piece and called in adjustments to the spotter aircraft. More smoke rockets were fired and additional strings of bombs were dropped. Corrections and bracketing continued until a Skyhawk on its fourth pass scored a direct hit on the gun position.

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