America’s secret supersonic spy drones flew over China in the 1960s

While we tend to think of drones as a very modern addition to the battlefield, the truth is, America's Defense Department has long been interested in the concept of unmanned aircraft. In fact, for a short window of time in the 1960s, America's supersonic, high-flying drones were already attempting reconnaissance flights over China.

In May of 1960, the United States was at a crossroads. A CIA pilot named Francis Gary Powers flying America's classified U-2 Spy Plane had been shot down over the Soviet Union at the start of the month. The ensuing international incident edged the world one step closer toward nuclear Armageddon, and President Dwight Eisenhower made the decision to cease all manned flights into Soviet Airspace as a result. With reconnaissance satellite technology under development but still years away from providing actionable intelligence, Lockheed's famed Skunkworks set to work on another possibility: unmanned flights over the Soviet Union.

In October of 1962, legendary engineer Kelly Johnson, whose career included designing both the U-2 Spy Plane and the SR-71 Blackbird, set to work designing what would come to be called the D-21: a long-range, high altitude drone that leaned heavily on technology developed for the SR-71's predecessor, the A-12.

The requirements Johnson was given by the CIA and U.S. Air Force were nothing short of extreme: the drone had to reach speeds of Mach 3.3–3.5, an operational altitude of 87,000–95,000 feet, and needed a fuel range of 3,000 nautical miles. Any modern-day engineer would tell you that such a project would still be daunting today, but Johnson had made a career out of accomplishing the seemingly impossible -- often with little more than a hand ruler and scratch paper for calculations.

His D-21 design could meet all the requirements set out for him, but in order to achieve such high speeds at such high altitudes, he had to use a ramjet engine that couldn't function until it was already flying high in the sky. As a result, plans were drawn up to deploy the drone from a variant of the A-12, dubbed the M-21 Blackbird.

With a wingspan of just over 19 feet and a length of nearly 43 feet, the D-21 looked a lot like someone had just hacked the end off of one of the A-12's wings, making the M-21 a matching aesthetic choice, if nothing else.

The D-21 carried a single high-resolution camera that would snap photos over a pre-programmed flight path. It would then eject the film canisters, which would drift down via parachute and float in water. The plan was to capture these canisters in the air, with Navy ships positioned to retrieve them from the water as a backup. The drone itself would then self-destruct to avoid being captured and reverse-engineered.

The first three test flights of the D-21 from the M-21 Blackbird went smoothly, but on the fourth attempt, the drone experienced an "asymmetric unstart" passing through the bow wake of its M-21 mothership. The two aircraft collided in mid-air at the blistering speed of Mach 3.25. Both pilots managed to eject, but one ultimately drowned before he could be rescued. The decision was made to scrap the M-21 mothership strategy and instead deploy the D-21 from beneath the wings of the B-52H bomber.

After a number of failures, Lockheed's D-21 completed its first successful B-52H-launched flight in June of 1968 and soon, the program moved into operational reconnaissance flights over China.

In all, four D-21s were launched from B-52Hs and sent into Chinese airspace on reconnaissance missions. Two of the drones completed their flights, but either failed to eject their film, or the film was deemed irretrievable. The other two flights were either shot down or simply disappeared shortly after launch.

Despite their failures over China, the D-21 program was significantly ahead of its time. A Mach-3 capable drone with an operational ceiling of 90,000 feet was an unheard of proposition in its day and remains impressive even in this new era of unmanned aerial vehicles.

The program was ultimately canceled on July 15, 1971, with the B-52s converted for use in the program returned to operational service.