Lockheed D-21 Stealth Drone
Number built: 38
Max speed: >Mach 3.3, 2,200 mph
Operational altitude: 90,000 feet
Begin Development: October 1962
Introduced: 1969
First flight: 22 December 1964
Retired: 1971
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.
Several successful test flights were made, followed by at least four unsuccessful operational D-21 flights over China.
Famed Skunkworks designer Kelly Johnson developed the concept of a long-range drone and specified speeds of Mach 3.3–3.5, an operational altitude of 87,000–95,000 feet, and a range of 3,000 nautical miles. It was intended to make a one-way trip, eject its camera payload at the end of the mission for recovery, then self-destruct.
Imagine doing the pre-programmed path pre-digital computers! And, without data telemetry, you had to recover the camera then destroy the aircraft.
Compare to 2025... 
My son and I saw the D-21 at the fantastic "Blackbird Airpark" at an annex of the Air Force Flight Test (AFFT) Museum at Edwards AFB. All aviation buffs should visit this place!
