The USAF acquired the Bronco primarily as a FAC aircraft. The first combat USAF OV-10As arrived in Vietnam on 31 July 1968 as part of "Operation Combat Bronco", an operational testing and evaluation of the aircraft. These test aircraft were attached to the 19th Tactical Air Support Squadron, 504th Tactical Air Support Group at Bien Hoa Air Base in South Vietnam. The test roles included the full range of missions then assigned to FAC aircraft, including day and night strike direction, gunship direction, bomb damage assessment, visual reconnaissance, aerial artillery direction, and as escorts for aircraft engaged in Operation Ranch Hand. The aircraft's ability to generate smoke internally was utilized for strike direction and "in four specific instances under conditions of reduced visibility, the smoke was seen by strike aircrews before the [OV-10A] [was] detected." Operation Combat Bronco ended on 30 October 1968.