The Battle of Lima Site 85, also called Battle of Phou Pha Thi, was fought as part of a military campaign waged during the Vietnam War and Laotian Civil War by the North Vietnamese People's Army of Vietnam (PAVN) and the Pathet Lao, against airmen of the United States Air Force (USAF)'s 1st Combat Evaluation Group, elements of the Royal Lao Army, Royal Thai Border Patrol Police, and the CIA-led Hmong Clandestine Army. The battle was fought on Phou Pha Thi mountain in Houaphanh Province, Laos, on 10 March 1968, and derives its name from the mountaintop where it was fought or from the designation of a landing strip in the valley below, and was the largest single ground combat loss of USAF members during the Vietnam War.
During the Vietnam War and the Laotian Civil War, Phou Pha Thi mountain was an important strategic outpost which had served both sides at various stages of the conflict. In 1966, the United States Ambassador to Laos William H. Sullivan approved a plan by the USAF to construct a TACAN site atop Phou Pha Thi; at the time they lacked a navigation site with sufficient range to guide U.S. bomber aircraft to their targets in North Vietnam. In 1967 the site was upgraded with the air-transportable all-weather AN/TSQ-81 radar bombing control system. This enabled American aircraft to bomb North Vietnam and Laos at night and in all types of weather, an operation code-named Commando Club. Despite efforts to maintain the secrecy of the installation, which included "sheep-dipping" of the airmen involved, the facility did not escape the attention of the PAVN and Pathet Lao forces.
Toward the end of 1967, PAVN units increased the tempo of their operations around Phou Pha Thi, and by 1968 several attacks were launched against Lima Site 85. In the final assault on 10 March 1968, elements of the PAVN 41st Special Forces Battalion attacked the facility, with support from the PAVN 766th Regiment and one Pathet Lao battalion. The Hmong and Thai forces defending the facility were overwhelmed by the combined PAVN and Pathet Lao forces.
Background
Phou Pha Thi is a remote mountain in Houaphanh Province, northeastern Laos. The mountain, which is about high, is located within the former Royal Lao Army's Military Region 2, and about from the border of the Democratic Republic of Vietnam and away from Sam Neua, the Pathet Lao capital. For the local Hmong and Yao tribes that lived in the area, Phou Pha Thi was a place of religious significance. They believed it was inhabited by spirits possessing supernatural powers to exercise control over their lives. The United States Air Force (USAF) saw Phou Pha Thi as an ideal location for installing a radar navigation system to assist pilots in their bombing campaigns in North Vietnam, and along the Ho Chi Minh Trail inside Laos.Chauhan, p. 22
Laos was a neutral country according to the International Agreement on the Neutrality of Laos signed on 23 July 1962. Therefore, the United States was prohibited from openly conducting military operations in the kingdom. Activities undertaken by the USAF in Laos had to be approved by the ambassador to Laos, William H. Sullivan. When the plan to install a navigation system on Phou Pha Thi Mountain was proposed, Sullivan initially opposed it as he thought that Laotian Prime Minister Prince Souvanna Phouma would not allow his country to be involved in an aerial offensive against North Vietnam. Souvanna Phouma did permit the installation, on the condition that it not be used or occupied by U.S. military personnel.Thompson, p. 102
In August 1966, the USAF installed a TACAN System, an autonomous radio transmitter that provided pilots and navigators with distance and bearing relative to the station on Phou Pha Thi. In 1967, under the code name Heavy Green, the facility was upgraded with the TSQ-81, which could direct and control attacking jet fighters and bombers to their targets and provide them with precise bomb release points. It began operating in late November 1967 as Operation Commando Club. To operate the equipment within the limitations imposed by the Laotian Prime Minister, USAF personnel assigned to work at the installation had to sign paperwork that temporarily released them from military service, and to work in the guise of civilian technicians from Lockheed—a process euphemistically called "sheep-dipping". In reality, they operated as members of the USAF Circuit Rider teams from the 1st Mobile Communications Group based at Udorn Royal Thai Air Force Base who rotated to the site every seven days.Chauhan, p. 23
Personnel working at the TACAN site were supplied by weekly flights of the 20th Special Operations Squadron, based at Udorn RTAFB in northeastern Thailand operating under the code name Operation Pony Express, using Lima Site 85, the airstrip constructed by the Central Intelligence Agency in the valley below. Hmong General Vang Pao, who spearheaded the allied war effort against North Vietnamese and Pathet Lao forces in Military Region 2, was entrusted with the task of guarding the facility using the Hmong Clandestine Army alongside CIA-funded Thai Border Patrol Police forces. Though substantial resources were invested to maintain the facility, the USAF command doubted Vang Pao's ability to defend the installation. Accordingly, all equipment had explosives attached so that if the site was overrun, it could be quickly destroyed. By late 1967, Lima Site 85's radar directed 55% of all bombing operations against North Vietnam.Hamilton-Merritt, p. 182
Prelude As USAF ground controllers were able to guide attacking aircraft against North Vietnamese targets in all types of weather, installation of the TSQ-81 radar system on Phou Pha Thi was considered to have been extremely successful during the final months of 1967. Yet a formerly top-secret after-action report credited Commando Club with guiding the following sorties:
Against North Vietnam Nov Dec Jan Feb Mar 1–10 Summary Total Missions 153 94 125 49 6 427 Missions Under Commando Club (TSQ-81) 20 20 29 27 3 99 Percentage Under Commando Club 13.0 21.3 23.2 55.1 50.0 23.2
At the same time, Commando Club was directing missions westward into Operation Barrel Roll's B Sector, as the North's forces bypassed LS 85 in their push deeper into Laos to attack Nam Bac.
Barrel Roll area Nov Dec Jan Feb Mar 1–10 Summary Total Missions 268 327 320 375 182 1,472 Missions Under Commando Club (TSQ-81) 1 67 23 142 165 408 Percentage Under Commando Club – 20.4 10.3 37.8 90.6 27.7
The trend of LS 85 being forced to use its capabilities toward defending itself instead of assisting offensive missions into North Vietnam is evident from the tables above. Successes of the system also brought about worries for the personnel on the ground. Major Richard Secord, who was responsible for the security of Lima Site 85, was concerned about the safety of the unarmed USAF technicians working there dressed as civilians. He requested Green Berets be assigned as on-site security. Ambassador Sullivan turned down the request. Sullivan repeatedly insisted the "civilian personnel" at Lima Site 85 should not be armed, but Secord decided to equip the technicians with weapons. M16 rifles, fragmentation grenades, concussion grenades, and other small arms were then brought in.Hamilton-Merritt, p. 178 Secord said that, given the site's meager defenses, he felt the site could not be held against a serious assault.Secord, Wurts, pp. 75–77
Secord's fears were justified, as USAF reconnaissance aircraft regularly flying over northeastern Laos in 1967 revealed that the paved roads constructed by the North Vietnamese were obviously approaching Phou Pha Thi. Road construction activities were observed along Routes 6 and 19, which connected Dien Bien Phu in North Vietnam with Phou Pha Thi and Nam Bac in Laos.
Realizing the PAVN would try to destroy the installation, Secord advised the US Embassy in Vientiane to evacuate all US personnel. However, high-ranking US officials insisted that Lima Site 85 should operate as long as possible, as it helped save the lives of US pilots every day it remained operational. In December 1967, a communist military offensive in the region was signalled by a series of skirmishes. On 15 December, CIA-led Hmong reconnaissance patrols detected both PAVN and Pathet Lao battalions moving against Nam Bac, at the time the stronghold of the Royal Lao Army.Chauhan, p. 24
On 16 December, two Pathet Lao companies overran Phou Den Din, only east of Lima Site 85. Shortly afterwards, Hmong units recaptured the village. Toward the end of 1967, US controllers at Lima Site 85 directed F-4, F-105 and A-1 fighter-bombers based in Thailand and South Vietnam in air strikes against North Vietnamese and Pathet Lao formations that were massing around the US facility at Phou Pha Thi. A-26 Invaders were called in for night missions, targeting movements of the enemy ground troops on Route 6 and Route 19. On 14 January 1968, the situation in northeastern Laos continued to worsen, as an estimated four PAVN infantry battalions captured the Laotian government's stronghold at Nam Bac. Despite the growing threat from North Vietnamese forces, the US military was still not permitted to reinforce the installation on Phou Pha Thi Mountain due to political sensitivities.
The defense of Lima Site 85 was assigned to two CIA paramilitary officers who led about 1,000 Hmong soldiers, with 200 men guarding the ridge line and the remaining 800 in the valley below. They were reinforced by a Thai Border Patrol Police battalion of 300 men.Chauhan, p. 25 In the first week of 1968, the combined PAVN and Pathet Lao forces probed Royal Laos Army positions in the area by launching several artillery attacks. On 10 January, a Pathet Lao patrol was driven from the area by the Hmong soldiers. Fearing the explosives attached to their equipment could be detonated by incoming artillery rounds, US technicians dismantled the charges and threw them over the cliff.
On 12 January, CIA spotters reported a four-aircraft formation flying in the direction of Lima Site 85. They were Soviet-made Antonov An-2 biplanes. Two aircraft continued towards Lima Site 85, while the others turned away. The Vietnam People's Air Force, in one of its few air attacks during the conflict, tried to destroy the radar at Lima Site 85. The An-2s flew over Phou Pha Thi, and their crewmen dropped 120 mm mortar shells through the aircraft's floor and then strafed their targets with 57 mm rockets mounted on the wing pods.Hamilton-Merritt, p.180 As they repeatedly attacked the facility, ground fire heavily damaged one AN-2, and it crashed into a mountainside. By now, CIA officers and US controllers at Lima Site 85 had managed to contact an Air America helicopter, which was faster than the Soviet-made biplanes. The Huey pilot Captain Ted Moore sighted the remaining An-2, and promptly gave chase. As he pulled alongside, flight mechanic Glenn Woods armed with an AK-47 assault rifle opened fire and caused the biplane to crash into a ridge.Hamilton-Merritt, p. 181