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The M-21 was basically an A-12 that was designed to carry and launch the expendable 10 ton D-21 (?mini-Blackbird?) unmanned reconnaissance drone, and two A-12s were built to M-21 standard to carry the drone. The main difference between the A-12 and M-21 models were that the M-21 had the sensor package in the ?Q?-bay behind the pilot?s cockpit removed to make way for a second seat for the Launch Control Officer (LCO).
An M-21/D-21 combination in flight. the D-21 has an aerodynamic cone covering
its ramjet exhaust,
suggesting this was a captured test flight only.
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| A D-21 drone on it's dolley on display at the USAF Museum at Wright Patterson AFB in Dayton Ohio. |
The D-21 looked like a half scale single engined Blackbird, albeit without a cockpit, and was powered by a Marquardt ramjet. Because the ramjet powerplant would only work at speeds above Mach 3, it was necessary to first get the D-21 up to that speed on the back of a Blackbird before the ramjet could be powered up. The first successful D-21 launch was carried out over the Pacific Ocean off California, where the drone was released and fired at Mach 3.2. Two further successful launch tests were conducted, with the drone flying some 1,600 miles (2,600 km) at up to 92,000 feet and Mach 5 on the third flight, and the concept was proved.
The fourth test flight ended in disaster when the D-21 drone got caught in the mothership's shock wave at launch and crashed back into the rear fuselage of the M-21 at Mach 3.25! Both the pilot and LCO amazingly survived the initial impact and high speed breakup of the M-21, but the LCO tragically drowned before he could be rescued. The M-21/D-21 program was immediately cancelled by Kelly Johnson, and the D-21 was subsequently modified to be carried beneath the wing and be launched with a rocket booster from a B-52H mothership.
D-21 drones eventually flew four operational unmanned missions over the Chinese nuclear test site at Lop Nor in the Gobi Desert, before being retired in July 1971 because of difficulties in retrieving the detachable sensor package in mid air at the end of a flight. A total of between 38 and 50 D-21s were built, and up to 17 examples survive in storage at AMARC at Davis-Monthan AFB in Tucson, Arizona. The surviving M-21 was transferred to the A-12 test unit at ?The Ranch?, where it ended its career and was placed into storage with the other A-12s in late 1968.
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