Lockheed M-21 (s/n 60-6940) mothership aircraft mated to D-21 photographic reconnaissance drone, approaching an aerial refueling probe, 1960s. The M-21, under Project TAGBOARD, was a modification of the A-12 OXCART airframe and was operated jointly by the Central Intelligence Agency and United States Air Force. Airframe 6940 was one of two M-21 airframes purpose-built rather than modified from existing A-12s.