The Siege at An Loc: How Air Resupply Helped Save the City

by LTC Len Funk, USA-Ret.

After mounting massive conventional warfare assaults near the DMZ and in the Central Highlands on 5 April 1972, Hanoi extended the deadly arm of the Nguyen Hue, or the 1972 Easter Offensive, to South Vietnam’s Military Region III (MR III), formerly known as III Corps. North Vietnamese Army (NVA) forces quickly overran Loc Ninh, a tiny district town in Binh Long Province near the Cambodian border. One week later, three NVA divisions, supported by tanks and massive amounts of artillery, launched an all out attack on An Loc, the capital of Binh Long Province, 60 miles north of Saigon.

The vital role that U.S. and South Vietnamese aerial bombing played in saving An Loc is well known. However, the much less publicized, but equally vital, U.S. Army and Air Force air resupply effort also played a major role in helping the South Vietnamese Army (ARVN) forces and their U.S. Army advisors defending An Loc survive a 70-day siege, a siege longer than either Vicksburg or Dien Bien Phu.

The North Vietnamese could not have picked a better time to attack in MR III. Since the drawdown of American troops began in 1969, the region had seen U.S. combat units dwindle to almost nothing. Between February and April 1972 alone, 58,000 troops and advisors returned to the U.S. This was the single largest troop reduction of the war and it came precisely when the NVA was building up for the Easter Offensive.

Those advisors that did remain in III Corps operated within the Third Regional Assistance Command (TRAC), headquartered at Long Binh outside of Saigon. TRAC, the distilled remains of II Field Force and the former III Corps Advisory Group, was commanded by the flamboyant, Pattonesque, World War II tank commander Major General James F. “Holly” Hollingsworth. In 1966-67 Hollingsworth had served as deputy commander of the 1st Infantry Division, whose area of operations included Binh Long Province, so he was familiar with the territory. In mid-1971 Hollingsworth returned to Vietnam as deputy commander of the U.S. XXIV Corps. By the end of the year he was on his way to Long Binh to command the last American advisors in III Corps. Given his reputation as a hands-on fighter, Hollingsworth was not only miscast for this managerial assignment, but he was under pressure from his old World War II friend, Military Assistance Command, Vietnam (MACV) Commander General Creighton W. Abrams to continue the troop drawdown and not endanger American lives. Yet withdrawing advisors from the increasingly dangerous situation in An Loc would send a signal of diminished American support of the South Vietnamese and would certainly weaken their resolve. Hollingsworth chose to defend An Loc but did not order his advisors to remain in the surrounded city. He evacuated those deemed nonessential along with the senior American advisor to select his combat advisory team. Only a handful of Americans remained in the tactical operations center with General Hung and the 5th ARVN Division staff.

By 1972, the advisory system in MR III, and in the rest of South Vietnam, was primarily a skeleton team sprinkled throughout the top of the ARVN officer corps. In combat units, advisors now interacted with their ARVN counterparts only at corps, division, and regimental levels. In elite units, such as airborne, rangers, and marines, advisors were still used down to the battalion level.

At An Loc, the 5th ARVN Division had a U.S. Army senior advisor with a small staff under him. The senior advisor was responsible for “advising” his counterpart on troop movement and deployment, a particularly crucial job during the drawdown because ARVN forces were spread thinly over areas previously covered by both American and South Vietnamese troops. The advisors also gathered intelligence from units in the field and sent it back to TRAC headquarters for analysis. However, as far as the South Vietnamese were concerned, the senior advisor was most valuable in his role as air support provider. As a result, the senior advisor spent much of his time plotting air strikes and coordinating them with TRAC headquarters.

When the 5th Viet Cong Division struck Loc Ninh on 5 April, the magnitude of the artillery barrage that preceded the attack was unprecedented in MR III. Two days later Loc Ninh fell and intelligence reports from the rubber plantations north of An Loc noted large numbers of NVA tanks already in place.

Air Force forward air controllers (FACs) reported heavy troop and truck movement particularly to the north of An Loc. They saw hundreds of civilians were fleeing rubber plantations, attempting to avoid NVA conscription. B- 52 strikes were placed wherever a troop concentration was reported. Gathering bomb damage assessment information, however, was difficult because the South Vietnamese would not patrol beyond An Loc’s city limits.

On 7 April, the NVA overran the Quan Loi airstrip located a mile and a half east of An Loc. The highway, Route 13, was cut, blocking the main road in and out of town. The city was surrounded by communist troops and isolated from the outside by road. Only helicopters and aircraft with pilots willing to risk flying through the enemy anti-aircraft batteries encircling the city could keep An Loc supplied with food and ammunition. The population of An Loc consisted of 15,000 persons, half military and the other half civilian. The resupply objective was 200 tons per day, including 140 tons of ammunition, 36 tons of rice and other rations, and 20 tons of water.

Early in the morning of 11 April, the ARVN 1st Airborne Brigade left neighboring Binh Duong Province by truck for Chon Thanh, the southernmost district in Binh Long Province. It was to dismount just north of Chon Thanh and continue the remaining twelve miles north toward An Loc on foot. Their mission was to sweep the area clean of the enemy patrols that might threaten the vital Route 13 supply line from Saigon. This elite ARVN unit never got close to its objective.

Nine miles south of An Loc, the ARVN troopers met a blocking force made up of a regiment from the 7th NVA Division. During the same period, 10-11 April, the 1st and 2nd battalions, 8th ARVN Regiment, as well as the regimental combat reconnaissance company, were flown into An Loc by the U.S. Army’s 1st Brigade, 1st Cavalry Division, the last remaining element of the famous airmobile division still in South Vietnam. During the next six days, under a canopy of B-52 strikes, the ARVN frantically continued reinforcing An Loc. Between 7-12 April, the Vietnamese Air Force’s (VNAF) 237th Helicopter Squadron, flying U.S. Army CH-47 Chinooks, completed 42 sorties, though limited to a single landing zone. Each sortie brought in approximately 3.5 tons. Some of the Chinooks were hit as they hovered for the few seconds it took to dump their cargo, but none were shot down by NVA fire. Then, on 12 April, an enemy mortar scored a direct hit on an ARVN Chinook. A few hours later, after another massive Soviet-style artillery barrage, the 7th Viet Cong Division, with T-54 tanks and trucks, launched the initial assault on the An Loc perimeter.

After the first assault, not only were the NVA able to occupy the northern half of the city, but they were able to move an anti-aircraft regiment immediately outside the An Loc defensive perimeter. All CH-47 deliveries were halted, and only fixed wing cargo planes attempted the dangerous flight into An Loc, where the drop zone (DZ) had shrunk to an area 1,000 yards by 750 yards. Thus, the ARVN began airdropping supplies. VNAF crews and transports, primarily C-123’s, made their first drops on 12 April. All drops were made during daylight and all were troubled by the enemy fire and small drop zones. Planes could only approach An Loc from the south, flying along Route 13. They usually flew in three-aircraft formations at 700 feet. Other airplanes released their loads from 5,000 feet or higher to avoid anti-aircraft fire. The crews used makeshift sighting devices or simply guessed where to drop their cargo. Lacking delayed parachute-opening devices, drops were usually off target and landed outside the defensive perimeter. After 27 C-123 and C-119 drops in the first three days of the siege (12-14 April), only 34 tons of the 135 tons dropped was recovered. Six transports took ground fire and on 15 April, a C-123 was shot down, killing all aboard, including the squadron commander. Four days later a second C-123 was shot down.

On 14 April, Military Assistance Command, Vietnam (MACV), decided to deploy the first USAF C-130s to An Loc. Two of the four-engine aircraft, using the Computerized Aerial Drop System (CARP), made their first run at dawn the following day. They circled the city until a FAC signaled to commence the dangerous run. Initially, no instruments were needed; pilots simply followed Route 13 from the south. As they approached the DZ, a 219 square-yard soccer field in the southern part of An Loc, the computer took over, releasing the supplies at a pre-arranged point. The first airplane roared over the target. As enemy guns opened fire, pallets of food and ammo crashed to the earth and the aircraft climbed up from the 600 foot drop altitude with only slight damage to the rudder.

After talking with the FAC on site, the second crew decided to surprise the enemy with an approach from a different direction. When the C-130 was thirty seconds from the release point, a wall of machine gun fire met the nose of the aircraft. The pilot struggled to control the shuddering transport under the impact of dozens of bullets. Rounds smashed the circuit panel in the flight deck, killing the flight engineer and wounding the navigator and co-pilot. The situation in the cargo hold was even worse. Incendiary rounds ignited some of the pallets of 155mm howitzer and 81mm mortar ammunition. The crippled C-130, flying on 2 engines, limped back to Tan Son Nhut Airbase north of Saigon. U.S. advisors at An Loc later reported that none of the 26 tons of supplies dropped by the two transports were recovered.

On 15 April, two more C-130s headed for An Loc. To counter enemy interception, communication crews used five different frequencies instead of one. The CARP system was abandoned because it required strict attention from the crew, which was preoccupied flying the airplane through the hostile fire. Instead they manually dropped the cargo load. Although the two aircraft were hit, they successfully dropped fifteen tons of ammunition and supplies within the area controlled by the ARVN.

On 18 April, NVA anti-aircraft fire nearly downed another C-130. With the right wing burning, one engine out, and another on fire, the crew ditched the cargo and managed to crash land near Lai Khe.

The situation on the ground at An Loc was grave. On 13 and 15 April, twenty-four NVA tanks led major ground assaults into the city. Allied weapons stopped the enemy armor, but communist forces held the northern half of the city. Despite total allied air superiority, the enemy continued to pound the remainder of the city with an average of 1,000 artillery rounds per day. In addition to the heavy shelling, the defenders of An Loc faced other serious problems. Significant amounts of the air-dropped supplies landed within enemy lines. As a result of the shelling and the misdirected supplies, the defenders’ morale declined considerably.

Although aerial supply efforts were going nowhere, new developments inside An Loc took some pressure off the Air Force. Originally, U.S. Army ground advisors estimated that it would take 200 tons a day to sustain the garrison. The highest priority was small arms ammunition and 105mm howitzer rounds. The NVA quickly eliminated the need for the howitzer rounds by destroying all the ARVN artillery in the first few weeks of the siege. Water requirements also eased when a series of brackish wells were found inside the perimeter. U.S. Army advisors now felt they could survive on 65 tons per day.

The Air Force then tried night drops. On 24 April seven C-130s headed for An Loc with lights out. All made it in safely and dropped their loads, but accuracy was marginal, and at night, stray pallets were more difficult to recover. On 25 April eleven C-130s tried another night mission. The first four aircraft that rolled over the target were met by heavy anti-aircraft fire. One C-130 took several hits, quickly lost altitude, and crashed two miles south of the DZ, killing all onboard. All subsequent missions that night were called off, and ten additional missions were cancelled the following night due to inclement weather. Two drops were made on the 27th and most of the cargo was recovered. Both aircraft, however, suffered damage from enemy ground fire.

For the next seven days Air Force C-130s made only night drops. Out of thirty-seven missions, U.S. advisors “recovered” thirty-five tons, “possibly recovered” ninety-six tons, and “probably lost” 350 tons. They also reported that enemy barrages over the DZ continued to increase in volume and intensity. Over fifty percent of the C-130s making night drops were hit by enemy fire. With many aircraft damaged and the loss of a third C-130 with its crew on 4 May, the Air Force decided to end standard level drops. Thus far, three C- 130s had been lost and thirty-eight had been hit by enemy fire over An Loc.

The disappointing results of the night drops were not a reflection on the ingenuity of the participants. Several expedients were devised to aid in spotting the soccer field DZ. One relied on aerial flares for illumination, but unfortunately, this method silhouetted the aircraft for the NVA gunners. ARVN troops also used portable runway lights and blazing cans of gasoline to mark the DZ.

Termination of the night drops coincided with the desperate conditions on the ground within An Loc. Food and ammunitions stocks were critically low, and medical and sanitation conditions were rapidly deteriorating.

On 29 April the NVA fired the first SA-7, a shoulder-fired surface-to-air missile, at U.S. aircraft in Quang Tri Province near the DMZ. With the possibility of SA-7s near An Loc, the return of low-level resupply operations was unthinkable.

C-130 crews met this challenge with the first “high velocity” drop at An Loc on 8 May. One thousand pound bundles were rigged to 15-foot slotted parachutes. These chutes were designed to stabilize descent at roughly one hundred feet per second, approximately four times the normal impact velocity. There was no low opening function, which eliminated the need for a delay mechanism. Accuracy remained high because of the high-speed descent.

On 3 May the Air Force resumed High Altitude, Low Opening (HALO) drops at An Loc with fair results. The following day, using a modified HALO method, two C-130s dropped sixteen bundles. No parachutes opened prematurely and all but one bundle landed in the DZ.

On 8 May, twenty-foot slings were inserted between each parachute and its load to allow a better chance for proper chute filling. The results were positive. The incidence of unopened parachutes dropped to five percent on 10 May and remained negligible thereafter.

Eleven high velocity missions were made at An Loc between 8-10 May. Out of 140 bundles 139 hit the DZ. The NVA launched their last major ground assault on 10 May. When drops resumed on 13 May, the suitability of high velocity drops became even more obvious, despite the fact that descending bundles could be dangerous to those on the ground. On several occasions, loads of artillery rounds detonated on impact and fuel drums ruptured after the parachutes malfunctioned. While small arms ammunition usually survived the drops, medical supplies proved too fragile for this kind of drop, even under optimum conditions. On 29 May an even more reliable chute was introduced, a slotted twenty-two footer which carried a one-ton bundle.

Strong communist forces remained around An Loc during June, but ARVN relief forces were making a slow approach toward the city along Route 13, clearing the ground lines of communication and establishing fire bases. On 11 June VNAF helicopters began bringing replacements into An Loc, and between 13-14 June, U.S. Army choppers lifted 1,400 fresh troops into the besieged city. Beginning on 18 June, the defenders slowly pushed out of the rubble that had once been An Loc and the South Vietnamese Command declared the siege over, despite the fact that Highway 13 remained closed.

After mid June, drops into An Loc were cut to two per day. Although pressure on An Loc decreased in late 1972, communist forces continued to hold Quan Loi airfield and threatened movement along Route 13. C-130s continued to resupply An Loc by air until December 1972. Both sides maintained defensive positions in the region as the likelihood of cease-fire increased. In MR I, General Truong, the “Savior of Hue,” emerged as the hero of the Easter Offensive. In MR II, the redoubtable Colonel Ba, who held Kontum, was the hero. On the southern front, in MR III, the hero was Major General Hollingsworth. It was he who saved An Loc. He strengthened the resolve of the ARVN corps commander when the situation looked grim. He visited An Loc daily during the worst of the shelling and encouraged both the ARVN troops and American advisors defending the city. Above all, largely because of his rapport with MACV Commander General Abrams, Hollingsworth was able to divert B-52 strikes from MR I and MR II to An Loc when the city was most seriously threatened. It was Hollingsworth and his deputy, Brigadier General John R. McGiffert, an artillery officer who had also served in the 1st Infantry Division in 1966-67, who personally planned the B-52 and tactical air strikes that saved An Loc.

Like Stalingrad, Dien Bien Phu, and Khe Sanh, An Loc was a classic siege with the garrison supplied entirely by air. Unlike Stalingrad and Dien Bien Phu, the end results were much better for the besieged at An Loc. Through the coordinated efforts of the U.S. Army advisors under Hollingsworth; the air resupply effort, B-52 attacks, and tactical air strikes by the Air Force; and the determined resistance of the besieged ARVN forces, the South Vietnamese and their American allies were able to withstand a massive assault by the NVA and save the city of An Loc.

For more information on the Siege of An Loc and the Easter Offensive read: Jeffrey J. Clarke, Advice and Support: The Final Years; LTG Phillip B. Davidson, USA (Ret)., Vietnam at War; Dale Andrade, Trial by Fire; and Donaldson D. Frizzell and Ray L. Bowers, Eds., “Airpower and the 1972 Spring Invasion,” in Air War – Vietnam.