YF-12A - Early March 1998   At the time of my visit to the USAF Museum in Dayton, this was the only A-12 in the museum. The YF-12 was developed in the 1960s as a high-altitude, Mach 3 interceptor to defend against supersonic bombers. Based on the A-12 reconnaissance aircraft, the YF-12A became the forerunner of the highly-sophisticated SR-71 strategic reconnaissance aircraft.