By late January 1968, American intelligence sources detected the presence of 20,000 or more North Vietnamese soldiers in the vicinity of Khe Sanh. 1 American tactics were to allow the enemy to surround the 26th Marine Regiment (Reinforced) at Khe Sanh, to mass their forces, to reveal troop formations and logistic routes, to establish storage and assembly areas, and to prepare siege works. The result would be the most spectacular targets of the Vietnam War for American firepower.

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.3 NIAGARA would be composed of two elements. NIAGARA I was an comprehensive intelligence-gathering effort to pinpoint the available targets, while NIAGARA II was the coordinated shelling and bombing of these targets with all available air and artillery assets.

The efficacy of the firepower available to the Marines at Khe Sanh was a function of the accuracy of the target selection processes. The intelligence section (S-2) of the 26th Marine Regimental headquarters company was tasked with the responsibility of acquiring targets. S-2 had knowledge of the siege strategy employed by the North Vietnamese Army (NVA) at Dien Bien Phu in 1954 and Con Thien in 1967. These historical lessons were used to predict the behavior of the enemy at Khe Sanh.

Various sources were utilized to develop a view of enemy activity around the Khe Sanh plateau. Sources external to the immediate battlefield included intelligence reports from the Military Assistance Command (MACV) in Saigon, III Marine Amphibious Force (III MAF) headquarters in Da Nang, as well as the headquarters of the 3d Marine Division at Phu Bai.

Intelligence was generated locally via a variety of means. Hundreds of acoustic and seismic sensors were seeded around the combat base. This comprehensive sensor system cost approximately a billion dollars and was credited with reducing the number of Marine deaths sustained during the fighting by fully fifty per cent. 4 By Marine estimates, forty percent of the raw intelligence obtained at Khe Sanh was provided by the sensor system. 5 Ground and aerial observers provided visual evidence of enemy activity, as did photo reconnaissance. Crater analyses from incoming rocket, mortar, and artillery rounds were conducted to determine the likely source of the attacks. Shell/flash reports yielded additional targets. Infrared imagery and analysis of intercepted enemy communications were also used.

Marine reconnaissance patrols, Army Special Forces, Central Intelligence Agency personnel, and the MACV Studies and Observation Group (SOG) all provided input to the 26th Marines S-2. The CIA Joint Technical Advisory Detachment and SOG obtained their information from casual encounters from villagers; from regular paid agents, including Rhade and Bru Montagnards, and from locals who desired being hired as agents of the U.S. intelligence community around Khe Sanh.

Likely or confirmed targets were then attacked by the firepower available to the Marines at Khe Sanh. It was the base Fire Support Coordinating Center (FSCC) that was responsible for coordinating the array of supporting arms.

After making the trip down the Ho Chi Minh Trail through Laos, the North Vietnamese established various forward logistic bases within a few thousand meters of the combat base. During periods of darkness the Communists dug shallow trenches leading from their supply points toward the U.S. positions. American intelligence noticed this trenching system around February 23, 1968. Once the trenching system had been constructed close to the base, secondary trench lines branched off and paralleled the Marine perimeter. These close-in, secondary trenches were constructed 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 air strikes. These fires slowed down NVA trenching efforts, but were unable to halt them completely. From a logistic standpoint, it was impossible to deliver sufficient munitions to saturate the trenching systems with massed artillery fire. Consequently, the FSCC altered its tactics. The NVA were permitted to construct their trench systems close to the base in order to simplify pin-pointing and killing them with supporting arms.

The sensor system quickly proved its worth. During the night of February 3-4, the sensor arrays indicated the presence of up to 2,000 North Vietnamese soldiers in the vicinity of Marine hill outposts northwest of the combat base. Defensive artillery fires were ordered against these troop concentrations. Sensor monitors 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 incident is one of the earliest examples in warfare of a ground attack entirely thwarted on the basis of remote sensor data.

By crater analysis, it was possible to confirm locations that were suspected based on other intelligence sources; detect the presence and location of enemy batteries; assist in counterbattery fires; and detect the presence of new types of enemy weapons, new calibers, or new munitions. The direction of flight of a projectile can 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 from crater analysis techniques. A stick placed in the clay soil tunnel made by a dud round would point in the direction of origin, and the angle of the stick indicated the angle of fall. By measuring this angle and using the firing tables of enemy weapons types, counterfire personnel were able to compute the range of the enemy weapon. Inspections of shelled areas were made as soon as possible after the shelling.

Staff Sergeant Bossiz Harris, the acting gunnery sergeant of Mortar Battery, 1st Battalion, 13th Marines, was known to conduct crater analyses during incoming fire. This allowed the 1st Battalion, 13th Marine Fire Direction Center (FDC) to direct prompt return fire. Rapid and accurate counterbattery fire could force the enemy artillerymen to seek cover from American incoming, thereby curtailing their fire mission, as well as destroying NVA guns and gun crews.

In order to minimize the reaction time of the Marine and Army artillerymen at Khe Sanh, Colonel Lownds 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, who adjusted their tubes. This aiming process usually took less than forty seconds before a round was on its way. During the battle, 1st Battalion, 13th Marine guns fired 158,891 mixed artillery rounds in direct support of the 26th Marines at Khe Sanh.

Acquiring data on enemy troop locations was one thing; giving that data a correct interpretation 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. This information was interpreted as indicating NVA troop movements away from the combat base. Analysts examining sensor readout data concluded 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 the existence of a major target in the Khe Sanh TAOR. Photo analysts spotted a bank of radio antennas at a limestone cave complex in the DMZ northwest of Khe Sanh. Radio signals emanating from this group of caves showed it to be a major enemy headquarters. There was speculation that North Vietnamese Minister of Defense Vo Nguyen Giap himself was personally supervising the battlefield from this location. Repeated B-52 attacks by the U.S. Seventh Air Force were launched against the cave complex. These actions 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 complex headquarters remained in operation for several weeks.

One Marine spotter on Hill 881 South, Lance Corporal Molimao Niuatoa, was gifted with especially sharp vision. Niuatoa was scanning the landscape with a pair of 20-power naval binoculars when he noted the muzzle flash of a NVA artillery piece firing from a distance of 12,000 to 13,000 meters from his position. The location was noted by the spotter. As this gun position was beyond the range of Marine artillery, it could only be taken out with air strikes. An observation aircraft was directed into the general vicinity. This observer did not know the exact location of the gun and so fired a 2.75-inch smoke rocket in the general vicinity of the target. A Marine A-4 Skyhawk jet dropped a 500-pound bomb on the marking rocket. Niuatoa adjusted by noting the location of the billowing bomb smoke in relation to the artillery piece and called in corrections to the spotter aircraft. More smoke rockets were fired and additional strings of bombs were dropped. These corrections and bracketing continued until a Skyhawk on its fourth pass scored a direct hit on the gun position, yielding a series of secondary explosions.

After 1965, air power in South Vietnam was deployed to extend and compliment the effectiveness of field artillery. Although the 26th Marines possessed thirty artillery pieces as well as tanks and recoilless rifles, the fact that the base could only be supplied by air placed limits on the Marines' ability to saturate the Khe Sanh area with artillery-delivered munitions. It was airpower that would elevate the flood of firepower to Niagara-sized dimensions.

Khe Sanh had top-priority claim on all U.S. air assets in Southeast Asia. B-52s, personally directed by General Westmoreland from the Saigon MACV combat operations center, came from Guam, Thailand, and Okinawa. The Marines and U.S. Air Force provided fighter-bomber support from bases within South Vietnam. Naval aviators from Task Force 77 flew sorties from aircraft carriers in the South China Sea. The South Vietnamese Air Force and U.S. Army aviation also provided aerial support. From B-52s, originally designed as high-altitude strategic bombers for the delivery of nuclear weapons, to propeller-driven A-1 Skyraiders, the entire spectrum of American fixed-wing and rotary aircraft were deployed to support the 26th Marine Regiment at Khe Sanh.

Air representatives worked with their artillery counterparts in the Fire Support Coordination Center. Requests for air support were channeled through the Tactical Air Direction Center of the 1st Marine Air Wing (1st MAW) at Da Nang. If the 1st MAW could not fill a quota, liaison teams from other services were called upon for their support. The priority for air support was so high that at times the sky over Khe Sanh resembled "a giant beehive." 10 Upon arrival, aircraft were normally directed into a holding pattern until a ground controller or ground radar operator was free to direct the strike. Often these patterns extended upward to 35,000 feet with dozens of aircraft gradually corkscrewing their way downward as each flight delivered its ordnance and departed Khe Sanh airspace. A pilot might be directed to a succession of holding points only to end up with his fuel expended and his full load of ordnance still on board. If the pilot ran out of fuel before his turn came to deliver a strike, he was forced to jettison his bombs and return to base.

The contribution of U.S. Navy aviation reflected events in North Vietnam. Clouds that enveloped North Vietnam airspace forced a reduction in the number of Navy sorties there and the released planes and munitions were re-directed against targets around Khe Sanh. In February, about seventy-seven percent of Navy carrier sorties planned against North Vietnam were altered in this manner. One naval aviator who attacked the NVA trench system described the detonation of his 1,000-pound delayed action bomb as resembling the eruption of volcanoes. After collapsing fifty meters of trench, the NVA abandoned the building of assault positions in this area.

Close air support was employed against pinpoint targets in proximity of friendly troops. Usually there were fighter-bombers overhead at Khe Sanh around the clock. Tactical air controllers in light airplanes or helicopters maintained communications between strike pilots and troops on the ground. The tactical controller made a marking run by firing a smoke rocket or throwing a colored smoke grenade at the target to be attacked. When the strike pilot saw the smoke, dummy passes were made until the controller was satisfied the jets were lined up on the proper target. Bombing runs were executed and short corrections were made via radio until all ordnance was expended. The tactical air controller would then fly over the target to record the effectiveness of the strike. Battle Damage Assessments were relayed to the departing aircraft for intelligence debriefings upon return to base.

Ground-controlled radar bombing was employed in periods when the target could not be acquired due to bad weather. Radar controllers operated from a heavily reinforced bunker which contained fragile computer equipment and the TPQ-10 radar used to guide aircraft to their target. This radar emitted a beam which locked onto the aircraft. Using targeting data acquired from the FSCC, the controller programmed the computer with information on enemy position, ballistic characteristics of the ordnance, wind speed and direction, and other relevant data. At a predetermined release point, the controller instructed the pilot when to release his bombs. In specially-equipped aircraft such as the twin-engine Marine A-6 Intruder, the bombs could be released automatically by the ground controller. Marine controllers routinely directed strikes as close as 500 meters from friendly positions. The Air Force liaison officer felt strikes could be conducted to within fifty meters in case of emergency. 12 Marine air flew 7,078 sorties and delivered 17,015 tons of ordnance in defense of Khe Sanh, while the U.S. Air Force tactical aircraft contributed 9,691 sorties and 14,223 tons of munitions.

The most spectacular display of aerial power at Khe Sanh was provided by the B-52 Stratofortresses. With a payload of 108 500-pound bombs per plane, these Arc Light strikes were conducted against area targets such as troop concentrations, supply areas, and bunker complexes. These targets were programmed into on-board computers and were launched from altitudes above 30,000 feet. Arc Light bombing procedures were based on a grid system, with each block in the NIAGARA area represented by a one by two kilometer box superimposed on a map. Three B-52s, composing one cell, could effectively blanket such a box with high explosives.

On average, every ninety minutes one three-plane cell of B-52s would arrive on location around Khe Sanh and be directed to a particular target by a controller. Several flights of B-52s could churn up boxes of terrain several thousand meters long. Many enemy casualties were sustained from concussion alone. In some instances, NVA soldiers were found after an Arc Light strike wandering around in a daze with blood streaming from their noses and mouths. To catch these stunned survivors above ground, artillerymen at Khe Sanh often placed massed artillery fire into the Arc Light target area ten to fifteen minutes after the departure of the heavy bombers.

Arc Light attacks delivered a total of 59,542 tons of munitions from 2,548 sorties during the siege. 14 General Westmoreland was elated at the performance of B-52s, going so far as to maintain that the battle of Khe Sanh was won by the officers and men of the 3d Air Division (B-52). According to Westmoreland, the thing that broke the backs of the NVA at Khe Sanh was "basically the fire of the B-52's."

This high praise notwithstanding, Arc Light attacks had some limitations. A North Vietnamese soldier captured in April 1968, told his interrogators that his unit received frequent, timely, and accurate warnings of impending B-52 attacks. These alerts came either by radio or telephone and usually provided two hours' notice, sufficient for the NVA to depart the planned strike area. The NVA prisoner was not certain as to the origin of these warnings. Possibilities include Soviet intelligence-gathering trawlers operating in the Pacific and the interception of communications sent to or from the MACV combat operations center at Tan Son Nhut air base near Saigon.

The Target Intelligence Officer at Khe Sanh, Captain Mizra M. Baig, felt that Arc Lights were an accurate weapon which could be employed around Khe Sanh much the same as other supporting arms. However, since requests for B-52 strikes were submitted fifteen hours prior to the drop, Arc Lights could never be as responsive or flexible as tactical air and artillery. Techniques were developed by the FSCC to combine and compliment the strengths of aerial and artillery support. One such technique was the Mini-Arc Light.

When intelligence data indicated the presence of NVA units in a certain region, the FSCC computed a 500 by 1,000 meter box in the center of the suspected assembly area or likely route of movement. Two A-6 Intruders, each armed with twenty-eight 500-pound bombs, were placed on station. Army 175mm guns at the nearby artillery bases at Camp Carroll and the Rockpile initiated the Mini-Arc Light by pouring sixty 150-pound rounds into one half of the block. Thirty seconds later the A-6s unloaded their ordnance in the middle of the block. At the same time, the artillery at Khe Sanh poured an additional two hundred artillery and mortar rounds into the target area. Fire coordination was such that bombs and artillery shells hit at the same instant. When properly saturated with munitions, enemy soldiers caught in the zone "simply ceased to exist."

The Mini-Arc Light could be put into effect in about 45 minutes. To reduce reaction time even further, a Micro-Arc Light was executed. The block size was reduced to 500 by 500 meters. Any aircraft on station could be used for bombing. The Micro could be planned and executed within ten minutes. Twelve to sixteen 500-pound bombs, thirty 175mm artillery rounds, and 100 mixed lighter artillery rounds from Khe Sanh batteries could be unloaded on the target block within ten minutes. On an average night, three to four Minis and six to eight Micros were executed in the vicinity of the Khe Sanh Combat Base.

Because the Marines at Khe Sanh were surrounded by North Vietnamese, the base could neither be supplied nor evacuated by ground operations. Consequently, an effective method of aerial resupply was vital to the continued existence of the base. The principal source for supplies destined for Khe Sanh was Da Nang, a thirty minute flight. C-130s and C-123s provided the bulk of the supplies. Transport crews used speed offloading techniques to minimize the time they spent on the ground at Khe Sanh. When weather or hostile fire prevented transport aircraft from actually landing at the airstrip, parachute and various cargo extraction systems were employed to permit the unloading of cargo without putting the planes' wheels on the ground.

The Marine hill outposts, originally supplied from the base at Khe Sanh at the beginning of the siege, were thereafter served by externally-loaded helicopters flying from the Marine base at Dong Ha. Air Force and Marine crews en route to Khe Sanh flew the last few miles through a wall of enemy anti-aircraft fire - maintenance men at Da Nang noted 242 holes in one C-130 before they gave up counting.

As tactical air supported the Marines on the ground, so too did it accompany transport aircraft on their supply missions into the Khe Sanh TAOR. North Vietnamese antiaircraft guns in calibers up to 37mm were dug into the hills around Khe Sanh and menaced the existence of the aerial highway leading to the base. By March, the danger from enemy fire was so acute that all transports were provided with tactical air escorts. Air planners drew on their maps a line indicating the flight path of a cargo plane from the time it dropped below 3,500 feet above ground until it regained that altitude after disgorging its cargo. The potential danger area from which a 37mm gun could hit a plane was calculated. Fighter bombers were directed against known or potential enemy gun positions using 20mm cannon and fragmentation bombs. These attack runs commenced when the cargo planes reached an elevation of 1,500 feet above the ground.

In clear weather, two fighters laid down smoke screens for concealment on both sides of the flight path of the incoming transports. During the siege, every 37mm gun emplacement was repeatedly attacked until intelligence showed the gun to be destroyed or abandoned. More than 300 antiaircraft sites were reportedly destroyed. 20 When considered necessary, Air Force F-4 Phantoms equipped with cannon were kept in the area to provide combat air patrols to disincline the North Vietnamese Air Force from intervening in the fighting around Khe Sanh. Carrier-based aircraft bombed airfields in North Vietnam that short range enemy MiGs would have had to use to attack the Marine positions.

General Westmoreland was certain the North Vietnamese intended to overrun the Marine base at Khe Sanh as they had done at Dien Bien Phu. If so, air power was instrumental in denying victory to the Communist forces. Weather and other considerations prevented accurate measurement of the damage sustained by enemy forces from Operation NIAGARA. Photo reconnaissance and direct visual observation credited NIAGARA forces with causing 4,705 secondary explosions, 1,288 enemy killed, 1,061 structures destroyed, 158 damaged, 891 bunkers destroyed, 99 damaged, 253 trucks destroyed, and 52 damaged. Enemy personnel losses were estimates; they could not be confirmed since an actual body count was not possible. Westmoreland's Systems Analysis Office produced four models from which its analysts concluded that total NVA casualties - killed and wounded seriously enough to require evacuation - numbered between 9,800 and 13,000 men. The generally cited figure of 10,000 casualties represents half the number of NVA believed committed to attacking the Khe Sanh Combat Base at the beginning of the fighting there. 10,000 casualties represents fifty-nine percent of the number of enemy killed in all of I Corps during the 1968 Tet Offensive.

The one billion dollars worth of aerial munitions expended by the U.S. during the siege totaled almost 100,000 tons. That amount equaled almost 1,300 tons of bombs dropped daily, and represents an expenditure of five tons for every one of the 20,000 NVA soldiers initially estimated to be committed to the fighting at Khe Sanh. 22 This expenditure of aerial munitions dwarfs the amount of munitions delivered by artillery, which totals eight shells per enemy soldier believed to have been on the battlefield.

General Giap claimed Khe Sanh was never of particular importance to the North Vietnamese. According to Giap, it was the U.S. that made Khe Sanh important because the Americans had placed their prestige at stake there. 23 In the larger scheme of things, the fighting at Khe Sanh was of little lasting significance. Before the bombs and shells of Operation NIAGARA stopped falling on the Khe Sanh battlefield, U. S. President Johnson ordered severe restrictions on aerial and naval attacks against North Vietnam, declared the readiness of the U.S. to begin peace discussions to end the war, and declined to seek reelection to the presidency. In June 1968, the base at Khe Sanh was abandoned by the Americans. Ultimately, the U.S. would learn that it was unable to win at the conference table what it could not win on the battlefield.