The A-12 was produced from 1962 to 1964 and flew from 1963 to 1968. It was the precursor to the twin-seat U.S. Air Force YF-12 prototype interceptor, M-21 launcher for the D-21 drone, and the SR-71 Blackbird, a slightly longer variant able to carry a heavier fuel and camera load. The A-12 began flying missions in 1967 and its final mission was in May 1968; the program and aircraft were retired in June. The program was officially revealed in the mid-1990s.