Ca.1962: TOS USAF as a T-37B, then modified as the prototype T-37C. 1963: Converted to YAT-37D as prototype for a counter-insurgency attack aircraft; was given engines of 2400 lbst and six underwing pylons as well as the wing-tip fuel tanks. 12/64: Flown to the Air Force Museum. 8/66: Returned to service with the USAF due to high losses of A-1 Skyraiders in Vietnam. Testing was resumed as the aircraft was redesignated YA-37A as a prototype for the A-37A, and later brought up to A-37A standards. 7/70: Flown to the Air Force Museum.