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Operation Niagara: Siege of Khe Sanh

Originally published by Vietnam magazine. Published Online: June 12, 2006 
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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.

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.

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.

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.

After 1965, air power was deployed in South Vietnam to increase the effectiveness of field artillery. Although the 26th Marines possessed 30 artillery pieces as well as tanks and recoilless rifles, the fact that the base could only be supplied by air limited Marine ability to saturate the Khe Sanh area with artillery-delivered munitions. It was air power that would raise 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 Westmoreland from the Saigon MACV combat operations center, came from Guam, Thailand and Okinawa. Marine and Air Force fighter-bombers provided support from bases in South Vietnam, and Navy aviators from Task Force 77 flew sorties from aircraft carriers in the South China Sea. The VNAF and U.S. Army aviation also provided aerial support. From B-52s, originally designed for high-altitude strategic delivery of nuclear weapons, to propeller-driven Douglas A-1 Skyraiders, aircraft from the entire spectrum of American aircraft were deployed to support the 26th Marines at Khe Sanh.

Air representatives worked with their artillery counterparts in the FSCC. Requests for air support were channeled through the Tactical Air Direction Center of the 1st Marine Air Wing (MAW) at Da Nang. If the 1st MAW could not fill a quota, liaison teams from other services were called upon for their support. At times the sky over Khe Sanh was said to resemble a giant beehive. 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 holding patterns extended upward to 35,000 feet, with dozens of aircraft corkscrewing their way downward as each flight delivered its ordnance and departed the 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.

In February 1968, about 77 percent of the Navy carrier sorties planned against North Vietnam were redirected against targets around Khe Sanh due to clouds that enveloped the North Vietnam airspace. One naval aviator who attacked the NVA trench system said the detonation of his 1,000-pound delayed-action bomb resembled a volcano eruption. After U.S. air support collapsed 50 meters of trench, the NVA abandoned building assault positions in the area.

Close air support was sometimes employed against targets close to friendly troops. Tactical air controllers in light airplanes or helicopters maintained communications between strike pilots and troops on the ground, and fighter-bombers were over at Khe Sanh around the clock. The 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, and battle damage assessments were relayed to the departing aircraft.

During bad weather, ground-controlled radar bombing was employed. Radar controllers operated from a heavily reinforced bunker that contained fragile computer equipment and the TPQ-10 radar used to guide aircraft to their target. This radar emitted a beam that 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 to release his bombs. In specially equipped aircraft such as the twin-engine Marine Grumman A-6 Intruder, bombs could be released automatically by the ground controller. Marine controllers routinely directed strikes as close as 500 meters to friendly positions. The Air Force liaison officer felt strikes could be conducted to within 50 meters in case of emergency. Marine pilots flew 7,078 sorties and delivered 17,015 tons of ordnance in defense of Khe Sanh, while U.S. Air Force tactical aircraft made 9,691 sorties and delivered 14,223 tons of munitions.

The most spectacular display of air power at Khe Sanh was provided by the B-52 Stratofortresses. The B-52s had a payload of 108 500-pound bombs per plane, and these strikes, code-named Arc Lights, were conducted against 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, in which each block in the Niagara area was represented by a box superimposed on a map. Three B-52s, composing one cell, could effectively blanket a box with high explosives. On average, every 90 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 cells of B-52s could churn up boxes of terrain several thousand meters long. Many enemy casualties were due to concussion alone. In some instances, NVA soldiers were found after an Arc Light strike wandering around in a daze, blood streaming from their noses and mouths. To catch these stunned survivors, artillerymen at Khe Sanh often brought massed artillery fire down onto the Arc Light target area 10 to 15 minutes after the heavy bombers departed.

Arc Light attacks delivered a total of 59,542 tons of munitions from 2,548 sorties during the siege. General Westmoreland was elated at the performance of B-52s. According to Westmoreland, the thing that broke the back of the NVA at Khe Sanh was 'basically the fire of the B-52s.'

Arc Light attacks had some limitations, however. An NVA soldier captured in April 1968 told his interrogators that his unit received frequent, timely and accurate warnings of impending B-52 attacks. The alerts came either by radio or telephone and usually provided two hours' notice. 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 Light was an accurate weapon that could be employed around Khe Sanh much the same as other supporting arms. However, since requests for B-52 strikes had to be submitted 15 hours prior to the drop, Arc Light raids could never be as responsive or flexible as tactical air and artillery. The FSCC developed ways to combine the strengths of aerial and artillery support. One technique was the Mini-Arc Light.

When data indicated that NVA units were 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 28 500-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 60 150-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 200 artillery and mortar rounds into the target area. Fire coordination was such that bombs and artillery shells hit at the same instant.

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 a 500-by-500-meter area. Any aircraft on station could be used for bombing. Twelve to 16 500-pound bombs, 30 175mm artillery rounds, and 100 mixed lighter artillery rounds from Khe Sanh batteries could be unloaded on the target block within 10 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 NVA, the base could be neither supplied nor evacuated by ground operations. An effective method of aerial resupply was vital, and the base's principal source for supplies was Da Nang, a 30-minute flight away. Lockheed C-130s and Fairchild C-123s delivered the bulk of the supplies. Transport crews used speed-offloading techniques to minimize time 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 used to unload cargo without putting the planes' wheels on the ground.

The Marine hill outposts, originally supplied from the base at Khe Sanh, were thereafter served by 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.

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. NVA anti-aircraft guns in calibers up to 37mm were dug into the hills around Khe Sanh and menaced 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 for a cargo plane from the time it dropped below 3,500 feet 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 descended to 1,500 feet.

In clear weather, two fighters would lay smoke screens to conceal 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 anti-aircraft sites were reportedly destroyed. When necessary, Air Force F-4 Phantoms equipped with cannon were kept in the area to discourage 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 MiG aircraft would have had to use to attack the Marine positions.

General Westmoreland was certain the NVA 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. Photoreconnaissance 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. Without a body count, enemy personnel losses were estimates. Westmoreland's Systems Analysis Office produced four models from which its analysts concluded that total NVA casualties–killed or 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 to have attacked the Khe Sanh combat base at the beginning of the fighting there. The number also represents 59 percent of the number of enemy killed in all of I Corps during the Tet Offensive.

The $1 billion of aerial munitions expended by the United States during the siege totaled almost 100,000 tons. That was almost 1,300 tons of bombs dropped daily–five tons for every one of the 20,000 NVA soldiers initially estimated to have been committed to the fighting at Khe Sanh. 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 Vo Nguyen Giap claimed that Khe Sanh was never of particular importance to the North Vietnamese. According to him, it was the United States that made Khe Sanh important because the Americans had placed their prestige at stake there. 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, President Lyndon B. Johnson ordered severe restrictions on aerial and naval attacks against North Vietnam, declared the readiness of the United States to begin peace discussions to end the war and declined to seek re-election to the presidency. In June 1968, the base at Khe Sanh was abandoned by the Americans. Ultimately, the United States would learn that it was unable to win at the conference table what it could not win on the battlefield.



This article was written by Peter Brush and originally published in Vietnam Magazine.

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8 Responses to “Operation Niagara: Siege of Khe Sanh”


  1. 1
    Michael D. Cooley says:

    Sounds like the military version. The fact is that our artillery could reach about three feet beyond our lines while VC artillery could hammer us without limit. What saved our butts was military air power and the fact that we wouldn't allow our outposts to be taken. Jiap made a huge miscalculation by believing that the same tactics that had worked against the French would work against a bunch of Marines. He had fought the Marines before, he should have known better.
    With respect to U.S. stategy, the only thing coming out of Westmorland was just don't lose. He didn't do crap. All the support came out of IIIMAF. I guess when the rest of us who were there have all died off your version will become valid.

  2. 2
    tex says:

    Thank god for the "dusters" from the army to keep the assholes at bay.

    Good article.

  3. 3
    JayVee says:

    With sincere apologies to anyone who'll take offense, I'm a person who still believes there should be limits to the killing in war. Blasting stunned and bleeding men to pieces with massed howitzer fire sounds like some sort of atrocity to me, even taking into account the fact that the defenders of Khe Sanh didn't have the space to hold prisoners, nor the men to guard them even if they could have been captured. I'm sure there are all sorts of reasons for doing what was done, probably fully justifiable under doctrines of necessity, etc., but this sort of slaughter (and the matter-of-fact way in which it's reported) still makes my blood run cold. In case you're wondering, I'm a (non-combat) veteran, and certainly no apologist for the VC or NVA.

  4. 4
    im2old2run says:

    It is not for anyone to judge..save the men who stood where the ground shook under their feet and the smell was so thick they could swim in it…..The knowledge that tactical nuclear munitions were considered an option…read the whole history…makes me aware of just how desparate the situation was.It is a fact that the FCB Khe Sanh was surrounded…cut off…under siege…In the hours of kill or be killed…What these men had to do there did not prove who was right…It proved who was left…Live with it…I do.

  5. 5
    joe says:

    usa usa usa

    • 5.1
      NVA ALL THE WAY says:

      My opinion on the matter is, the NVA had us out gunned, out maned, and they where more popular with the peasants. We had poorly made weaponry and we didn't know how to handle the oppositions guerilla tactics. The way i see it, we just didn't want it bad enough… And I know that sounds bad, but we bombed and burned our way through the war but that can only get you so far. We even used Dioxin, a chemical compound that messed with our chromosomes and the enemies equally. Our M-16 was prone to jamming and needed constant repair, the enemies AK-47 on the other hand is much more reliable and can be counted on. These are just a few reasons why we lost the war.

      • 5.1.1
        88 Bravo says:

        The politics of it can't go beyond opinion, especially on an internet comment board, but facts need to be straight. The M-16 was a better weapon than the AK-47 immediately after jamming problems in 1965 with the addition of the chromed barrel and correct maintenance was begun. B-52's caused massive NVA casualties and I believe made the NVA give up their siege. The most important thing was the remote sensor data that made it difficult for the NVA to mass for assaults.

  6. 6
    Michael Covington says:

    Actually the U.S soldiers won the war but the government was to scared to finish what they had started and so abandoned Vietnam but we had crippled them and had pushed them back into Laos north Vietnam and the government had actually made plans to land an invasion force in north Vietnam and were going to sweep through north Vietnam all the way down into Saigon and destroy all the communist resistances. so just so you know our army won but the government was full of a bunch of quitters oh and also in the process leaving behind men who most likely died in an N.V.A p.o.w camp beat and tortured to death.



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