The Lockheed D-21 is an unmanned or "drone" aircraft designed to carry out high-speed, high-altitude strategic reconnaissance missions over hostile territory. It is a product of the Lockheed "Skunk Works" program that developed the A-12, YF-12, and SR-71 "Blackbird" manned aircraft in the 1960's.


Originally, the D-21 was designed to be launched from the back of a modified A-12 (redesignated M-12) carrier aircraft. The first flight of the D-21/M-12 combination took place on December 22, 1964, but the first D-21 release from an M-12 did not occur until March 5, 1966. (2) more launches were successful, but on July 30, 1966, a D-21 collided with the M-12 after release, destroying both aircraft and resulting in the death of one of the M-12's crew members. No further "piggyback" launches were attempted.


A new launch system was developed using modified B-52H aircraft as carriers. The new D-21 configuration (designated D-21B) had dorsal mounting hooks for carriage under the B-52's wing, and a solid rocket booster for the initial acceleration required to start the ramjet engine. The first launch from a B-52 took place on November 6, 1967, but the D-21 crashed. Several flights followed in 1968 with mixed success.


The first operational launch was on November 9, 1969, but the D-21B was lost. Several successful operational missions were flown over the next (2) years, but the D-21 program was highly classified and details have not been released. The program was canceled in 1971 and the D-21s were placed in storage.