The Gary Powers incident of 1960 changed the way the United States spied on the Soviet Union. The subsonic, high-flying spyplane was downed by a Soviet Surface-to-Air Missile (SAM) that ended in the destruction of the aircraft and the capture of an American while elevating the mistrust witnessed between the two parties for decades. As such, thought was being given to developing fast-flying, high-flying unmanned concepts that could outrun / out-fly Soviet missile designs. The drone would serve the Central Intelligence Agency (CIA) service of the United States government to help keep a military advantage over the enemy.
Lockheed returned with its D-21 drone - a development that utilized many qualities of its A-12 high-altitude reconnaissance platform (detailed elsewhere on this site). The A-12 was the forerunner to the classic Mach 3-capable SR-71 "Blackbird" spyplane (also detailed elsewhere on this site) and followed its all-black appearance while utilizing special Radar Absorbent Material (RAM) skinning and a blended wing-body design. The D-21 actually looked the part of a single A-12 engine nacelle complete with a shockcone-like structure making up the nose assembly. It sported a single vertical tail fin and a double-delta wing mainplane form.
In theory the drone would be air-launched from the dorsal spine of an M-21, a variant of the A-12 developed exclusively for the role of drone "mothership" (hence its "M" designation). The airframe added a support pylon over the aft fuselage section on which to mount the D-21 drone and a second cockpit for the Launch Control Operator (LCO) crewman was added. The D-21 was detached by the crew when appropriate and traveled about on pre-determined waypoints - its payload strictly camera in nature. After completing its photographing of key enemy targets, it would fly to a preset rendezvous point and jettison its payload by parachute. The parachuting package was then to be picked up by a slow-flying Lockheed JC-130 "Hercules" transport aircraft for its return trip. Meanwhile, the D-21, designed as an expendable air vehicle, would self-destruct completely.
First flight of D-21 prototype was on December 22nd, 1964 - the unit was originally designated as "Q-12" with USAF hopes of also turning it into a useful cruise missile. Speeds were in the range of Mach 3.3 to Mach 3.5 and operating altitudes could reach up to 95,000 feet with a range out to 3,500 miles. To contend with the high speeds in play, the D-21 relied on skilful use of titanium at key sections. The attention paid to radar-absorbent materials and stealth design would keep the drone from being easily registered on enemy tracking software and hardware. A Honeywell avionics package was fitted as was an Inertial Navigation System (INS).
Power was from a ramjet engine developed by Marquardt Corporation. This powerplant became the RJ43-MA20S-4, a modified version of its RJ43-MA-11 series original designed to power the Boeing CIM-10 "Bomarc" SAM weapon. Since ramjet engines lacked the power to produce thrust from "zero-speed", the speed of the M-21 mothership in-air would be used by the D-21 drone to gain its initial velocity (before the ramjet could take over). Two A-12 aircraft were set aside for M-21 conversion.
Testing proved the D-21 drone largely unreliable. The fourth launch saw the unmanned vehicle detach and strike the tail section of the M-21 mothership, leading to its complete loss. While the two crew jettisoned safely, the launch officer drowned upon landing. This marked the final test launch of the D-21 from the M-21 platform so an alternative plan was drawn up to have the D-21 unit air-launched from under the wing of a specially-modified Boeing B-52 "Stratofortress" heavy bomber. Initial speed would be gained from the B-52 itself as well as through use of a rocket booster fitted to the drone. A pair of B-52H bombers were modified to a mothership standard.
Changes produced the "D-21B" designation and a first launch was recorded on September 28th, 1967. However this test proved a failure as the D-21B detached from its pylon mid-flight before an actual launch could be enacted. Testing continued into early 1968 but progress was slow and shown the whole arrangement to be lacking in consistent reliability. A successful launch was finally had on June 16th of that year but more failures continued to dog the program.
Despite this the D-21B was placed into limited service with the USAF/CIA. It conducted four total missions during its time aloft but all centered on communist China and not the Soviet Union. The first stopped responding and continued on a straight course into Soviet territory before crashing, being recovered by the enemy and thoroughly dissected. The second was able to drop its photographic payload but its parachute failed and the package was lost in the ocean. The third mission saw the same result - though the parachute deployed the recovery aircraft failed to collect the descending package in time. The final sortie over Chinese airspace came on March 20th, 1971. Again the D-21's control failed and sent the airframe crashing into enemy territory where it was promptly recovered and studied for whatever value it held.
The D-21 program came to an end in July of 1971 when it was finally realized that the arrangement was not a viable spying solution. Thirty-eight total D-21 drones of both marks were made and twenty-one of this stock was used - either successfully or not. The remainder ended in storage for a time before being sent to the scrap heap or to museums around the United States to be preserved as showpieces. Its intended high-flying, high-speed spy role was eventually overtaken by more advanced, space-based satellites placed in orbit by the American space program while the SR-71 and U-2 spy planes continued to provide decades of more reliable, faithful service all the while drones were continually being advanced along their own developmental lines.