“The 66-day battle of Khe Sanh, which began in January 1968, became a classic defensive operation for U.S. forces. It tested American concepts of defense and demonstrated that good fire support could effectively neutralize a superior force.” —Major General David Ewing Ott, USA (US Army Vietnam Studies: Field Artillery 1954-1973)
The North Vietnamese 1968 Tet Offensive was designed to be the knockout blow that would defeat South Vietnamese military forces, inspire a popular uprising against the South Vietnamese government, and force the Allied troops under the command of U.S. Army General William Westmoreland, Military Assistance Command Vietnam (MACV) to evacuate the country. A prelude to the communist campaign was the conquest of the remote base camp in the U.S. Marine I Corps Tactical Zone, Khe Sanh.
Khe Sanh was located in the northernmost South Vietnamese province of Quang Tri, about six miles east of the Laotian border and fourteen miles south of the Demilitarized Zone. Established in 1962 and initially occupied by Special Operations Forces, it was designed for surveillance, not interdiction, of enemy traffic down the Ho Chi Minh Trail. In 1966 General Westmoreland, over Marine objections, ordered it expanded to a battalion-sized base camp complete with airstrip. In 1967 it was expanded and reinforced to regimental strength.
Guns at Khe Sanh
In late 1967, Marine patrols observed stepped up North Vietnamese activity in the region, with evidence that large numbers of communist troops were remaining instead of typically transiting south. On 2 January 1968, about three weeks before the Vietnamese Tet holiday and truce were to begin, a Marine reconnaissance patrol attacked a six-man North Vietnamese Army patrol just outside the Khe Sanh defensive perimeter, killing five. Among the dead were an NVA regimental commander and his operations officer. The official Marine history concluded, “The fact that the North Vietnamese would commit such key men to a highly dangerous, personal reconnaissance indicated that Khe Sanh was at the top of the communists’ priority list.” Westmoreland interpreted the incident to mean that thousands of enemy troops were in the area and that Khe Sanh held the opportunity for finally bringing about the decisive engagement against the communists that he had long desired. The entire 26th Marine Regiment under the command of Colonel David Lownds was tasked with the defense of Khe Sanh. It was the first time since Iwo Jima that all three battalions of the regiment were together for a combat operation. Westmoreland planned to use the Marines as “bait” to lure the NVA into battle where they would be destroyed by superior American firepower. Anticipating that the Marines would be cut off, Westmoreland planned to use superior American air power to resupply and augment the defenses of the base. In the days leading up to Tet, additional men, including the South Vietnamese 37th ARVN Ranger Battalion, and supplies were air lifted to Khe Sanh. Approximately 3,000 troops were located in the base camp with 3,000 more split among positions on the nearby hills 950, 881, 861, and 558, so named for their height. Each garrison was supported by artillery. For the siege, the NVA had assembled two regiments of the 325C Division, veterans of Dien Bien Phu, and two regiments of the 320th Division. They would be supported by the 304th Division, an armored regiment, and two artillery regiments. All told, the NVA had committed from 20,000 to 30,000 troops for the operation.
The siege began on 20 January when a patrol between hills 881 North, held by the NVA, and 881 South, held by the Marines, led by Captain William Dabney made contact with elements of the NVA. The following day, the enemy launched an assault of hills 881S and 861. Enemy artillery damaged the airstrip and scored a major success when rocket and shellfire hit the main ammunition dump, leaving the Marines desperately short of shells. Despite incoming barrages and anti-aircraft fire, six C-130 cargo transports successfully landed later that day on the still-damaged air strip and discharged 24 tons of cargo, mostly artillery shells. For his troops to successfully hold out, Colonel Lownds estimated that he would need 160 tons of supplies per day.
The vital role that air power and artillery performed in the successful Marine defense of Khe Sanh cannot be overstated. During the siege there were times when approximately half of all air assets in the theater were tasked with the support of the Marines at Khe Sanh. There is no question of the value and importance of the many air strikes on enemy positions. But even more important was the Air Force’s ability to conduct aerial resupply operations. Westmoreland later wrote, “The resupply of Khe Sanh stands as the premier air logistical feat of the war. At no time during the siege did the defenders experience a serious supply shortage.”
Regarding artillery fire during the battle, 158,981 rounds of various calibers were fired on enemy positions and attack points. A total of 46 artillery pieces were used including five batteries of Marine artillery composed of three batteries of 105 mm howitzers, one battery of 4.2 inch mortars, and one battery of 155 howitzers. The Marines were supported by four batteries of Army 175 mm guns, all from the 2d Battalion, 94th Field Artillery. One battery was at a base codenamed “Rockpile” located about nine miles north-northwest of Khe Sanh, and the other three were based at Camp Carroll about thirteen miles northeast. All supporting arms fire was coordinated from Khe Sanh itself by the fire support coordination center (FSCC) operated by the 1st Battalion, 13th Marines (Artillery) and the direct air support center (DASC).
The complexity of the FSCC operations during the siege is indicated by the description of an average night’s pattern of preplanned fires by a target intelligence/information officer: “Combined TOTs (time on targets) from nine batteries totaled 4-6; separate battalion TOTs, Army 4-6 and Marine 10-15; battery multiple volley individual missions, 40-50; battery H&Is (harassment and interdiction) 20-30. Normal one-gun, one-round H&Is were not used; this type of fire was of little value. Marine and Army artillery were employed in target areas and at ranges to reduce to a minimum check fires caused by the arrival of MPQ (radar guided) and reconnaissance aircraft. Later, as we learned finesse, air was given the targets south of the base and west of the maximum range of the 175 mm guns; 1/13 was given any targets whose range required a maximum ordinate of 14,000 feet (altitude of an MPQ controlled air strike), and the 175 mm guns were assigned to targets to the north, northwest, and east of the base.”
FSCC’s ability to provide timely and accurate fire on numerous targets simultaneously was made possible by the Field Artillery Digital Automatic Computer (FADAC). First Lieutenant Carlton B. Crenshaw of Company C, 1/13, would receive the Bronze Star with “V” device and his second Purple Heart while stationed on Hill 881S during the siege. A few days after the siege had begun, Crenshaw, on night watch duty in the Charlie Battery command bunker had an opportunity to see the FADAC in action. In a letter home he wrote, “At about 10:00 our battalion fire control center called and needed support for another Marine recon unit that was surrounded. We had a new computer called FADAC that was able to do many things simultaneously. It gave us four simultaneous missions to be supported by eight artillery guns from my battery. In essence they provided a box of artillery protection for our Marines. The fire mission went on for hours as the box moved to cover the movement of the Marines back to the combat base.”
Easy clearance procedures for fire missions meant artillery could swiftly respond to changing tactical situations regardless of weather. Unless friendly aircraft were above the target area, artillery rounds could be striking enemy positions within forty seconds after the call for fire was made.
Support fire was organized into four responses, three-sided artillery box, mini Arc Light, micro Arc Light, and direct fire against targets of opportunity. North Vietnamese Army doctrine called for battalion attacks in column formation. Lt. Crenshaw described one use of the artillery box. In general the fire support coordination center used three batteries of the 1/13 to execute the three sides of the box around second echelon troops designed to support the enemy’s lead battalion during the attack, hemming the reserves. The fourth, open, side faced friendly lines. A fourth battery from 1/13 closed this fourth side with a rolling barrage that moved up and down the box like a piston in a cylinder. Simultaneously, the center placed a secondary box around surrounding enemy backup units. Four Army 175 mm batteries were responsible for two sides, about 500 meters outside the primary box. If weather conditions permitted, air strike missions, sometimes including B-52 Arc Light missions, supported the barrages. The combination of back and forth piston and side to side accordion salvo action proved devastating. Lead assault units would come under organic 81 mm mortar and 106 mm recoilless rifle fire when they came within range. When NVA commanders of the lead assault units attempted to call in support or reinforcements for an effective schwerpunkt, they discovered that their reserves were already under heavy combined arms attack.
Mini Arc Light missions were used against area targets and were the responsibility of the assistant fire support coordinator. Similar to a regular B-52 Arc Light mission, the value of a mini Arc Light mission was that it could be organized and employed more rapidly, generally within forty-five minutes. Once a target, such as an enemy troop staging area, was identified, the assistant fire support coordinator plotted a 500 x 1,000 meter block in the suspected area or across the anticipated march route. Two Intruder tactical aircraft, each armed with twenty-eight 500-lb. bombs, were then called in for a radar-guided bomb run. As the same time, batteries at Khe Sanh, the Rockpile, and Camp Carroll were alerted. Thirty seconds before the Intruders were about to drop their bombs, Army 175 mm batteries fired a sixty-round salvo concentrated on half the block. As the Intruders dropped their bombs down the middle of the block, Marine batteries directed fire on the second half of the block. Flight and trajectory times of all ordnance were computed so that all would strike simultaneously, saturating the block.
More rapid still was the micro Arc Light, which could be put into effect within ten minutes. Conducted essentially the same way, the micro Arc Light used less ordnance and over a smaller, 500 x 500 meter, area.
The direct fire against targets of opportunity was used by Marine artillery on Khe Sanh. The effectiveness of this method was demonstrated by Marine howitzers located on Hill 881S northwest of Khe Sanh. At one point during the siege, an alert machine gunner on Hill 881S saw a twenty-man NVA column, with troops carrying mortar tubes, climbing the slope of Hill 758, south of the Marines’ position. An initial salvo, from 1,200 meters, successfully hit a number of the enemy. When the survivors gathered around their fallen comrades, the Marines shoved aside their defensive parapets, depressed their gun tubes for a downhill shot, and fired off about a dozen rounds, killing all the enemy troops.
The B-52 Stratofortress was not generally regarded as a close air support asset. But, with a 27-ton payload of 500- and 750-pound bombs, they proved enormously effective in that role during the siege. Even a near miss by an Arc Light mission was devastating. In a study of the effectiveness of combined artillery and airpower at Khe Sanh, Captain John A. Hamilton, Jr., USA, wrote, “The concussion from a B-52 attack was so violent that fatal casualties were produced from concussion effects alone.” Applying the rule of thumb of one meter distance per each pound of TNT in a bomb, a 500-pound bomb could be dropped as close as 500 meters from a friendly position. This capability prevented the NVA from massing large numbers of troops close to Marine lines, particularly at night. Often after an Arc Light mission, 1/13 batteries would wait a maximum of twenty minutes before saturating the bombed area with artillery fire, inflicting additional casualties on the dazed enemy troops.
NVA used a number of types of artillery including tube and rocket. Soviet-built 122 mm rockets were launched mostly from positions on Hill 881N. Tube artillery in the form of 130 mm and 152 mm batteries were located on Co Roc Mountain in Laos. Marine positions on Hill 881S were ranged by NVA 120 mm mortars. In a tactic used fourteen years earlier at Dien Bien Phu, it’s believed that the NVA emplaced the 120 mm mortars at precise angles in tunnels in order to repeatedly hit one specific target. It is one explanation for why only Hill 881S received 120 mm mortar fire and why the communist mortars were never found and knocked out of action.
Communist shelling was often intense. One day alone, 1,370 shells landed on Khe Sanh. Lt. Crenshaw wrote that by the eight day of the siege, “Our hill reminds me of pictures that I have seen of trenches used by French, English, and German troops during World War I. Within a few days nothing will be left above the ground level.” Marines continued to dig foxholes and bunkers. But even deep bunkers with reinforced roofs proved little protection against NVA 120 mm mortar fire. In a letter home, Crenshaw noted, “The bunker next to mine took a direct hit with a 120 mm mortar yesterday which went about three feet of overhead protection and wounded two Marines in there.”
Enemy artillery fire was immediately answered by either counterbattery fire or air strikes or a combination of both. The Marine official history of the siege noted the extraordinary dedication of the Marine artillery officers in returning fire. In one example, the executive officer of the 1/13 “ignored the heavy barrage and raced from one shell hole to another analyzing the craters and collecting fragments so that he could determine the caliber of the enemy weapons as well as the direction from which they were being fired. Much of the counterbattery fire was a direct result of his efforts.”
The NVA made its greatest attempt to capture Khe Sanh the night of 29 February-1 March. Intelligence determined that the enemy had massed a significant force, later believed to be a battalion from the 304th NVA Division, and it was moving toward the eastern side of the Marine perimeter which was defended by the 37th ARVN Ranger Battalion. The FSCC quickly called in saturation fire missions on the projected enemy routes of march east and south of the perimeter. Within minutes tactical air, and mini and micro Arc Light missions added their destruction. Two and a half hours later, bomb payloads of the first full-scale Arc Light mission were dropped on the enemy troops. The NVA resolutely attempted three assaults on the ARVN line. The intensity of the combined ground, air and artillery fire was so great that at no time were the enemy troops able to reach, let alone breach, the outermost defensive line of barbed wire.
Montagnard tribesmen later reported that they discovered 200 to 500 enemy bodies stacked along the trails leading to Khe Sanh. Intelligence estimates concluded that an NVA regiment was virtually wiped out that night. The official Marine history of the siege concluded, “It was obvious that [the NVA troops] had been caught on the march and mangled by air raids and piston-like artillery concentrations. While many of the defenders of Khe Sanh never fired a shot, what was believed to be the long-awaited enemy onslaught came and passed with a whimper instead of a roar.” Though attacks against the base continued, the NVA never again staged a major attack on the base.
Two weeks later, intelligence determined that the enemy was pulling units away from the area. On 31 March, the Army’s 1st Cavalry Division arrived at Khe Sanh, relieved the Marine force, and commenced Operation Pegasus, the fifteen-day air assault operation that ended the battle of Khe Sanh. A final assessment by intelligence estimated that two crack NVA regular divisions were effectively destroyed and that their destruction was primarily caused by American combined artillery and air attacks.
During the siege, Bravo Battery, 1/13, an oversize battery composed of six 105 mm howitzers and three additional howitzers from Charlie Battery, had fired more than 1,250 rounds in support of the Marines at Khe Sanh. 1st Lieutenant Fred McGrath remembered that near the end of February, “Colonel Lownds personally came to our position and thanked every Marine in the position for the superb fire support his regiment had received.” Lownds would later receive the Navy Cross for his role in the defense of Khe Sanh and accept for the 26th Marines the Presidential Unit Citation.
North Vietnamese Defense Minister and commander in chief of the North Vietnamese Army General Vo Nguyen Giap had gambled that he could overwhelm the Marine and ARVN forces at Khe Sanh the same way he had the French at Dien Bien Phu. He failed. The resolution of the infantry defenders, coupled with the enormous power of American artillery and aircraft demonstrated that even an isolated and encircled position could hold out against a superior enemy force.
In comparing the two sides’ operations, Captain Harry Baig, 26th Marines Target Information Officer at Khe Sanh, later said, “Colonel Lownds employed traditional Marine tactics and doctrine of the twentieth century against an enemy who chose to put his faith and fortune in usages of the eighteenth.”