In late 1965, with the buildup of U.S. airpower in South Vietnam, the existing air bases were becoming overcrowded. In September, plans to build an air base at Qui Nhon were suspended when the site conditions were found to be unsuitable. In January 1966 a site in Phù Cát District 24 km north of Qui Nhon was identified.[1] In late February 1966 Military Assistance Command, Vietnam decided to build a new jet-capable base at Phù Cát.[1]: 120 In April 1966 forces from the Republic of Korea ArmyTiger Division secured the area for base construction, with the construction crews arriving in May. The Vietcong harassed construction, with booby-traps and sniper fire killing 3 Korean soldiers.[1]: 155–8
On 23 December 1966 USAF units began moving to the half-completed base. At this time the runway was a 3,000-foot (910 m) long dirt strip while the taxiways and parking areas were covered in Pierced steel planking (PSP). The 459th and 537th Troop Carrier Squadrons both equipped with C-7A Caribous began operations from the base on 1 January 1967.[1]: 147 Base facilities by this time included wooden barracks, a mess hall, recreation facilities and utilities.[1]: 173 By late March 1967 a 10,000-foot (3,000 m) by 125-foot (38 m) asphalt runway together with sealed taxiways and parking aprons had been completed.[2] Later in the year a fuel line was constructed to the base, from a tank facility on the outskirts of Qui Nhon.[2]: 273
While based at Phù Cát, a detachment from the 416th TFS pioneered fast Forward Air Control (FAC) operations using two-seat F-100Fs under the code-name Commando Sabre and the call sign Misty.[4][1]: 265
In September 1967 a detachment from the 4th Air Commando Squadron equipped with 4 AC-47 Spooky gunships began operating from the base.[5] In September 1969 the 4th Air Commando Squadron ceased operating from the base and moved its forward operating base to Da Nang Air Base.[5]: 70
On 13 April 1969, Detachment 1 612th TFS left the base and was replaced by the 480th Tactical Fighter Squadron equipped with F-4D Phantom II combat aircraft which moved from Da Nang AB.[4] On 11 May the 174th TFS returned to the US, followed by the 355th TFS on 15 May. On 27 May the 416th TFS transferred to Tuy Hoa Air Base and the Commando Sabre Fast FACs were inactivated.[4]
On 24 June the 389th Tactical Fighter Squadron equipped with F-4Ds transferred to the base from Da Nang AB.[4] In November B Flight, 18th Special Operations Squadron (18th SOS) equipped with three AC-119K Stingergunships deployed to the base where they operated primarily against supply routes in Laos.[5]: 203 During 1969 40 concrete and steel "Wonderarch" aircraft shelters were constructed at the base.[2]: 452
In June the 459th Troop Carrier Squadron was inactivated. The 537th Troop Carrier Squadron was inactivated during the year, with its aircraft transferred to the South Vietnamese.[4] On 29 December "A" Flight, 17th SOS, was inactivated and its aircraft transferred to B Flight at Phan Rang AB.[5]: 219
On 31 August 1971 the 361st Tactical Electronic Warfare Squadron equipped with EC-47N/Ps departed from the base.[4] On 8 October, the 389th TFS flew its last combat mission. On 26 October its aircraft began returning to the United States. On 20 October the 480th TFS flew its and the 12th TFW's last combat mission. On 17 November 1971 the 12th TFW was inactivated.[4] On 30 November 1971 the 1883d Communications Squadron was reassigned and moved to Kincheloe Air Force Base, Michigan.[3] On 5 December 1971 the base was formally turned over to the RVNAF.[8]
RVNAF use
A VNAF UH-1 at Phù Cát c.1970VNAF A-37s at Phù Cát c.1972
The 412st Transport Squadron formed at the base in 1970 operating C-7As inherited from the 537th Troop Carrier Squadron.[4]
The 243rd Helicopter Squadron operating UH-1 Huey gunships was based here.
On 17 May 1974 the base was attacked by the PAVN 2nd Regiment, 3rd Division. The attack was repulsed by the 108th and 263rd Battalions of the South Vietnamese Regional Forces.[9]
In mid-March 1975 Qui Nhon and Phù Cát AB were defended by the ARVN 40th Regiment and the Bình ĐịnhRegional Forces, however the 40th Regiment was soon redeployed to Khanh Duong to keep open the route for ARVN escaping from Buôn Ma Thuột. The 2nd Air Division provided air support for the 22nd Division and was also trying to destroy equipment abandoned during the evacuation of Pleiku.[10]
On the morning of 30 March the Regional Forces defending the base abandoned their positions and by afternoon the base was under attack by VC who were held back by the base security forces. With more VC gathering for renewed attacks, the base commander contacted the 92nd Air Wing at Phan Rang AB for help. The Wing commander, Colonel Le Van Thao organised a flight of 40 A-37 Dragonflies and they carried out a night attack on the base perimeter successfully breaking up the attack. On the morning of 31 March, the 2nd Air Division evacuated the base taking 32 aircraft, but abandoning a further 50; the PAVN/VC occupied the base that afternoon.[10]: 343–4