The Geneva agreement of July 1962 forbade foreign troops in Laos, so the American effort there was run by the CIA and flown by contract and borrowed crews. Its centre was Long Tieng. The agency began building it in 1962 for Vang Pao, the Hmong officer it had recruited in 1961, and by 1964 the valley had a 1,260 m strip under limestone karst, long enough for transports but never for jets. It carried two Lima Site numbers, 20A and 98, and grew into a town: Wikipedia, drawing on several authors, gives about 40,000 inhabitants in the late 1960s, which would have made it the second city of Laos, with estimates for the war years ranging from 30,000 to 50,000.

Secrecy held surprisingly long. In March 1970 TIME, whose correspondent had walked in uninvited, described Long Cheng as a top-secret, CIA-supported base for guerrilla operations against the Communists, where nobody else was allowed in. The same report put North Vietnam’s strength in Laos at 50,000, and Vang Pao’s guerrillas at 10,000.

Long Tieng was above all a logistics machine. From late 1962, according to the RLAF history drawn from Conboy, Vang Pao had about 200 primitive Lima Site strips built across the north, which Air America’s short-take-off aircraft and helicopters supplied from the valley; Air Force Magazine, in Walter Boyne’s 1999 account, credits the airline with keeping some 170,000 Hmong refugees alive with rice drops by 1970.

Two kinds of pilot made Long Tieng famous. The Ravens were US Air Force fighter pilots who volunteered to fly in civilian clothes, taking O-1 Bird Dogs and U-17s low over the jungle to find targets and mark them with smoke rockets. Air Force Magazine lists five Raven bases: Vientiane, Pakse, Savannakhet, Luang Prabang and Long Tieng. How many served is disputed: Wikipedia counts 161 including the earlier Butterfly controllers, the Ravens’ own association says 205 pilots and combat controllers, and Air Force Magazine says fewer than 300. Wikipedia gives 23 Ravens killed in action; Air Force Magazine and the association put losses at about 30 per cent.

The other pilots were Hmong. The Royal Lao Air Force trained its first two Hmong T-28 pilots, Lee Lue and Vang Toua, in Thailand in 1967, and formed a Hmong T-28 squadron at Long Tieng. Lee Lue led it from 1967 to 1969. Air Force Magazine credits him with up to ten missions a day and more than 5,000 sorties and calls him the Hans-Ulrich Rudel of the Laotian war; the RLAF history drawn from Conboy gives more than 1,000 sorties in under 18 months. He was shot down by anti-aircraft fire near Muang Soui, on 11 July 1969 according to Conboy and 12 July according to Boyne. Vang Sue succeeded him as wing leader until 1972.

The pace was relentless. During the North Vietnamese offensive of March 1970 one Hmong pilot flew 31 missions in a single day from Long Tieng, according to the RLAF history.

In early 1970 North Vietnam retook the Plain of Jars and pushed on. The advanced base at Sam Thong, a few kilometres from Long Tieng, was overrun on 18 March 1970, and B-52 sorties were stepped up to stop the main base falling. It held.

The second, larger attack came at the end of 1971. Under what Hanoi called Campaign Z, two North Vietnamese divisions, reinforced by at least 6,400 fresh troops, brought T-34 tanks and 16 130 mm field guns, which out-ranged the defenders’ 155 mm howitzers. The royalist garrison numbered about 5,000 in 19 battalions, ten of them Thai. Between 17 and 20 December the royalists lost 286 killed, 418 wounded and 1,500 missing by the account Wikipedia draws from Conboy and Morrison; 111 B-52 sorties were flown that month, and North Vietnamese fire and MiG-21s accounted for six T-28s and three F-4 Phantoms.

On 31 December 1971 the first 130 mm barrage hit Long Tieng and destroyed the main ammunition dump. By 5 January 1972 about 600 rounds had landed; Royal Lao Air Force facilities were damaged, the TACAN navigation beacon was moved 20 km south and flying was dispersed to Ban Son. The ridges above the valley were fought over into late January, but the base again survived. All casualty figures here are the royalist and American accounts; North Vietnamese figures were not found.

After the 1973 ceasefire the American money stopped, and in 1975 the coalition government collapsed. On 5 May 1975 Vang Pao was called before the Prime Minister, Souvanna Phouma, and told to cooperate with the communist forces; four days later the Pathet Lao press warned that the Hmong would be exterminated. The evacuation began in earnest on 13 May, when three American transports each flew four round trips to Udorn in Thailand with more than 65 people a time. On 14 May Vang Pao and his CIA case officer Jerry Daniels were flown out secretly by helicopter, and the airlift ended.

Wikipedia’s Long Tieng article puts the total lifted at 1,000 to 3,000, mostly military leaders and their families, carried in C-130s and C-46s; tens of thousands were left behind, and about 40,000 Hmong reached Thailand on foot by the end of 1975. The Lao People’s Army took over the valley. It was later folded into the Xaisomboun Special Zone, created in 1994 and dissolved on 13 January 2006, and Long Tieng is still described as a restricted military site. No source reached shows the Lao air force flying from it today.