The Lockheed D-21 is an American supersonic reconnaissance drone. The D-21 was initially designed to be launched from the back of an M-21 carrier aircraft, a variant of the Lockheed A-12 aircraft. The drone had maximum speed in excess of at an operational altitude of . Development began in October 1962. Originally known by the Lockheed designation Q-12, the drone was intended for reconnaissance deep into enemy airspace. The D-21 was designed to carry a single high-resolution photographic camera over a preprogrammed path, then release the camera module into the air for retrieval, after which the drone would self-destruct. Following a fatal accident when launched from an M-21, the D-21 was modified to be launched from a Boeing B-52 Stratofortress. Several test flights were made, followed by four unsuccessful operational D-21 flights over the People's Republic of China, before the program was canceled in 1971. Design and development In the 1960s Lockheed's secret Skunk Works developed the Mach 3 A-12 reconnaissance aircraft for the Central Intelligence Agency (CIA). After the shooting down of the U-2 piloted by Gary Powers in 1960, a number of different concepts were proposed as alternatives. Kelly Johnson, the leader of Skunk Works, developed the concept of a long-range drone that used much of the A-12's technology. In October 1962 the CIA and the United States Air Force (USAF) instructed Lockheed to study a high-speed, high-altitude drone concept. Johnson specified speeds of Mach 3.3–3.5, an operational altitude of , and a range of . It was intended to make a one-way trip, eject its camera payload at the end of the mission for recovery, then self-destruct. It had a double-delta wing similar to the A-12's wing design. The Q-12 was to be air-launched from the back of an A-12, and used key technology from the A-12 project, including titanium construction and radar cross-section reduction design features. Johnson wanted to power the Q-12 with a ramjet engine built by the Marquardt Corporation for the Boeing CIM-10 Bomarc long-range surface-to-air missile. Marquardt and Lockheed had already collaborated on several programs and had a close working relationship. The engine, the RJ43-MA-11, required modification, since it was only designed to burn as long as the missile needed to hit a target, while the Q-12's engine needed to operate at high temperatures for at least an hour and a half at high altitudes. The modified engine was designated RJ43-MA20S-4. A full-scale