The first T-37 converted for combat use were a small number of YAT-37D's in the early 1960s. After the cancellation of the program, one aircraft was retired to the USAF
museum. After things heated up in Southeast Asia, the program was restarted, and the aircraft returned to Cessna for modifications. 25 T-37 were converted to A-37A, went to Vietnam in 1967. Production of new A-37Bs. Started in1967. The USAF
procured most between 1968-1973 both for its service and for the VNAF
[South Vietnam]. Production lasted until 1976/77 for export orders.