LOCKHEED D-21B

One of the least known members of a family of aircraft that includes the SR-71 is the D-21 reconnaissance drone. The drone was designed to be launched from the back of a modified A-12, the first version of the Blackbird. A ramjet engine that requires very high speeds in order to operate powers the D-21. Initial testing began in 1963, however it was not until March 1966. Three successful test flights were made, but on the fourth flight the drone crashed into the launch plane and one of the two crewmen was killed. The drone was redesigned and fitted with a booster rocket. In this configuration it could be launched from a pylon mounted on a B-52. Testing of this version began in 1967 and eventually several operational missions were flown. The program was canceled in 1971.