During the Cold War, the US launched Project Constant Peg and acquired a number of Soviet aircraft to evaluate enemy aircraft and use them for adversary training – the most advanced of these fighter jets was the MiG-23 Flogger (the program ended in 1990). Constant Peg was part of the lessons learned in Vietnam. In 2023, the only airworthy MiG-23 remaining in the United States crashed in Michigan (that was a different MiG-23 purchased from Bulgaria after the end of the Cold War).