U-Tapao (Thai: อู่ตะเภา) is a compound of อู่ cradle or drydock and ตะเภา trade winds, and derives from the site having once been a shipyard for construction of ruea-tapao (เรือตะเภา), a type of argosy resembling a Qing Dynasty junk.

In 1965 the RTN was permitted by the Council of Ministers to build a 1,200-meter (3,940 ft) long airfield near U-Tapao village, Ban Chang District, in Rayong Province.

The agreement, reached on 2 March 1967, allowed 15 B-52s and their support personnel to be based at U-Tapao, with the provision that missions flown from Thailand would not over fly Laos or Cambodia on their way to targets in Vietnam.

In September 1966, two radio-relay KC-135A Combat Lightning aircraft and their personnel were ordered to deploy to U-Tapao to support air operations over North Vietnam.

[6] The expansion of U-Tapao RTN airfield began in October 1965; the runway was built in eight months,[7] and the base was completed slightly more than two years later.

The wing was charged with the responsibility of supporting refueling requirements of USAF fighter aircraft in Southeast Asia, plus conducting bombing missions on a daily basis.

[14][15] U-Tapao was initially more of a forward field than it was a main operating base, with responsibility for scheduling missions still remaining at Andersen AFB.

Cambodian bombing raids were initially kept secret, and both SAC and Defense Department records were falsified to report that the targets were in South Vietnam.

Following the opening of the Cambodian Campaign in late April 1970 the secret Menu bombings came to an end on 26 May and the USAF began overt operations against North Vietnamese People's Army of Vietnam (PAVN) and Viet Cong forces in eastern Cambodia.

Although there had been no campaign of strikes into North Vietnam since the end of Rolling Thunder, the Nixon Administration ordered a new air offensive, initially code named Freedom Train, later becoming Operation Linebacker, with relatively few restrictions on targets that could be hit.

The bombing raids, codenamed Operation Linebacker II, began on 18 December 1972 involving heavy attacks by almost every strike aircraft the US had in theater, with the B-52 playing a prominent role.

The U-Tapao-based B-52Ds were able to carry more bombs and perform more sorties than the other units which operated less capable versions and had to fly much further to reach targets in North Vietnam.

[20]: 263 The Paris Peace Accords were signed on 27 January 1973, however Arc Light strikes on Laos continued into April and on Cambodia into August.

On 23 March 1973 the USAF airlift control center at Tan Son Nhut Air Base, Saigon moved to U-Tapao becoming the Pacific Transportation Management Agency, Thailand, responsible for all C-130 operations in Southeast Asia.

U-Tapao based C-130s of the 374th Wing flew missions into Cambodia, South Vietnam, and a weekly flight to Hanoi in support of the International Commission of Control and Supervision until April 1975.

[18]: 627–9 On the afternoon of 12 April 1975, following the completion of Operation Eagle Pull, the evacuation of US nationals and allied Cambodians from Phnom Penh, an HMH-462 CH-53 carried Ambassador John Gunther Dean from USS Okinawa to U-Tapao.

[22]: 124 In the two years following the Paris Peace Accords, the PAVN underwent a massive rebuilding to recoup the losses suffered during their failed 1972 Easter Offensive.

An estimated 8,000 U.S. and third-country nationals needed to be evacuated from Saigon and the shrinking government-controlled region of South Vietnam, along with thousands of "at-risk" Vietnamese who had worked for the United States during the war.

Evacuation by civil and military fixed-wing aircraft from Tan Son Nhat had been taking place since early-March and continued until 28 April when PAVN artillery fire rendered the runways unusable.

[18]: 644 [25] On 12 May 1975, less than two weeks after the fall of Saigon, a unit of the Cambodian Khmer Rouge Navy seized the American-flagged container ship SS Mayaguez, taking the crew hostage.

The Khmer Rouge pinned the Marines in their landing zones, where they relied on air and naval gunfire for their survival, they were eventually evacuated as darkness fell.

[22]: 263 On 14 October 1973 following the 1973 Thai popular uprising former Supreme Court Judge Sanya Dharmasakti, then chancellor and dean of the faculty of law at Thammasat University, was appointed prime minister by royal decree, replacing the succession of staunchly pro-American and anti-Communist military dictatorships that had ruled Thailand previously.

[30] The 3rd Aerospace Rescue and Recovery Group left on 31 January 1976,[17]: 152  however the base remained under US control until it was formally returned to the Thai government on 13 June 1976.

[31] For several years, beginning in 1981, U-Tapao has hosted parts of Cobra Gold, jointly involving US, Singaporean, and Thai armed forces, and designed to build ties between the nations and promote interoperability between their military components.

[32][33] In addition, U-Tapao may be where Al Qaeda operative Abu Zubaydah and other renditioned detainees were interrogated, according to some retired American intelligence officials.

In 2012, a proposal for the United States National Aeronautics and Space Administration (NASA) to use U-Tapao to support weather research was rejected by the Thai government.

[38] In 2015, a Politico article reported that the United States Government rented space at U-Tapao from a private contractor for use as a "major logistics hub for the Iraq and Afghanistan wars."

"[39] Additionally in 2015, the Bangkok Post reported that the US would be allowed to station 16 planes at U-Tapao as part of a quake relief operation in Nepal.