Due to the agreement between the Soviet Union and the United States restricting the use of manned vehicles over the Soviet landmass,
this unmanned aircraft was developed. The drone was carried and launched by two A-12-like aircrafts called M-21s(moded SR-71's), and a number of B-52Hs.
The D-21 was released at high speed, and was separated from the M-21 by the use of ballistic charges. The concept behind the drone was
quite simple. It would fly over a landmass and eject the reconnaissance data before crashing, to be recovered shortly after by the Air Force.
This aircraft was never used operationally, and only 38 of these drones were built.
