The T-34A Mentor remained the standard USAF primary trainer until the introduction of the Cessna T-37 Tweet jet trainer in the late 1950s, replacing both the T-34A and T-28A. This also coincided with ATC's implementation of the Undergraduate Pilot Training (UPT) syllabus at various air force bases in the United States under ATC claimancy and phaseout and closure of the contract pilot training air bases. As they were replaced by T-37s, many T-34As were turned over to USAF aero clubs at air force bases in the United States and USAF air bases overseas. In all, the USAF acquired 450 T-34As.