... in 1963 the USAF went through serious exploration of adapting the A-12 (later called the SR-71 'Blackbird') into a Mach 3 longe-range interceptor. Tests were made with the AIM-47 'Falcon' air-to-air missile. The existence of the fighter-interceptor test program was also used as a cover for the primary use of the 'Blackbird' as a spy-plane. On 14 May 1965 the Air Force placed a production order for 93 F-12Bs for its Air Defense Command. But in the end only three YF-12s were built. One crashed and two were used by NASA for research.