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Lockheed D-21: The Drone Version of the SR-71

Whether it’s through military strikes carried out thousands of miles away, or the long-heralded day that we might see our Amazon packages arrive might arrive by air – drones are set to play a huge part in our future. But our story today dives back into the depths of the Cold War and focuses on a supersonic reconnaissance drone which arrived and almost as quickly disappeared 50 years ago. This is the rarely remembered Lockheed D-21.

The tale of the Lockheed D-21 is one of cutting edge technology, deeply shrouded mystery and close but no cigar. This was a drone that was launched from the back of an aircraft and could travel at an astonishing 3,600 km/h (2,300 mph). But it was also a piece of mechanical engineering that was well ahead of its time – maybe too far – and one that was perhaps not given the time to fully develop. Much of the details surrounding the drone have never been released and it remains somewhat of an elusive portion to the Cold War espionage story. 

1960’s

The Cold War saw a frenzy of espionage around the world, leading to many wonderfully devious tales of the west and the east attempting to outdo each other through covert operations. It became an obsession for both sides trying to steal secrets or simply get a glimpse at those areas well off-limits.

While many of the most famous tales involved spies on the ground, the action in the air was equally important and decidedly dangerous. The U.S had begun using a spy plane known as the U-2 from 1956 to photograph military installations across the USSR, but this came to a shuddering halt on 1st May 1960. 

Lockheed U-2 by D. Miller is licensed under CC-BY

As the surface-to-air missile slammed into Gary Powers’ U-2 aircraft, his options were bleak. Well over Soviet territory he knew that his plane was about to crash in the one area he had been specifically ordered to avoid at all cost. With him was a small needle of poison designed to kill him outright, and a self destruct switch which would have destroyed the aircraft before the Soviets could get their hands on it. For whatever reason, neither of these options were taken by Powers. 

The downing of its spy plane and subsequent parading of Powers in front of the Soviet media was a national embarrassment for the United States and one that they were keen to avoid again in the future. I suppose they did have the option of not spying on the USSR – but who are we kidding – they just needed to find a better way to do it. 

Development  

The U.S government turned to their trusty innovation factory, the Skunk Works division of Lockheed, which over time would produce a truly mesmerising array of next-generation military hardware, including the U-2, the Lockheed SR-71 Blackbird, the Lockheed F-117 Nighthawk, Lockheed Martin F-22 Raptor, and the Lockheed Martin F-35 Lightning II. 

But this needed to be something different and their proposal centred around a high-speed, high-altitude drone concept that would share many similarities with the Lockheed A-12 which was nearing completion. Specifications included a speed of Mach 3.3 – 3.5 (3,704 – 4,321 km/h – 2,531 – 2,685 mph) an altitude of 27,000–29,000 metres (87,000–95,000 feet) and a range of 5,600 km (3,500 mi). 

While no doubt it would have been great to get the drone back, it was decided that this would be a one-way flight. The D-21 was designed to reach, and photograph, a designated point before turning around and making its way back to a rendezvous point, ideally over the ocean. Here the small camera section of the drone would detach and parachute downwards before being picked up in mid-air by another aircraft, while the drone itself self-destructed. If that all sounds barely plausible, let me just remind you that this was the Cold War when the absolutely absurd was often attempted and frequently achieved. The mid-air aircraft recovery might sound like a bit of stretch, but it was actually already being done with C-130 Hercules used to retrieve film canisters deposited from satellites.

To make things even more complicated, it would need a degree of stealth to evade detection from radar, but fortunately, U.S technology was well on its way to this already. We’ve already done a video here on Megaprojects on the A-12 Archangel, which had its first flight in 1962, and many aspects of the D-21’s outer design were borrowed from it.  

By the end of 1962, a prototype of what was then known as Q12 was finished and had begun testing on its radar cross-section. The Q12 was powered by a ramjet engine, which is an air-breathing jet engine that uses its forward motion to compress incoming air and so pushes the jet forward. At the time the Marquardt RJ43-MA-20S4 engine was being used on the Boeing CIM-10 Bomarc long-range surface-to-air missile.  

When the Q12 was initially presented to the CIA and the U.S Airforce it received a mixed reaction. The CIA, no doubt with plenty on their plate at that time, were hardly enthusiastic about it, while the Air Force saw great potential in this supersonic flying robot. Eventually, the CIA was brought around and an order for a full-scale mock-up was placed with Skunk Works in March 1963.  

As I mentioned earlier, this was a drone that needed to piggyback on another aircraft, with its ramjet engine meaning it could not take off by itself. Skunk Works had finalised the A-12 a year before and two were requisitioned to act as transport planes for the Q12 – which was now named D-21. The converted A-12s became M-21s – so we now had an M for mother and D for daughter. 

The D-21 had a short wingspan of just 5.8 metres (19 ft), a length of 13.1 m (42 ft 10 in) and weight of 5,000 kg (11,000 lb) – roughly the same weight as a young African bush elephant. This was all without the booster that was later added, which I’ll go into a little later in the video. The result, not quite a plane, not quite a missile – the world’s first supersonic drone.   

Testing 

Testing any forward-thinking piece technology is bound to run into some complications and the D-21 had its fair share, which would eventually lead to tragedy. 

The first launch came on 5th March 1966 with the D-21 failing to spring clear of the M-21, which no doubt left the crew of the mothership peering warily around them. The second, just over a month later, was considerably better and reached both its desired height and speed before crashing because of a faulty hydraulic pump. The third flight proved to be the best, though this time the camera hatch did not release as planned because of an electronic failure. The D-21 was getting closer, but it was its fourth flight that caused a fatal accident that led to a complete re-think of the D-21 would be launched. 

On 30th July 1966, an M-21 once again climbed into the sky with a D-21 attached to it. All other test flights had been done on an outside loop, meaning the aircraft was essentially turning away from the released D-21, but the fourth flight called for everything to be done on a straight path.

Immediately following its detachment, the D-21 suffered an engine failure and slammed into the tail section of the M-21 – destroying both the aircraft and the drone. Both the pilot and the launch control officer were able to eject from the M-21 but they came down over the ocean and sadly Ray Torrick, the M-21’s LCO, drowned as he was engulfed by his parachute. 

Re-design    

The disaster of the fourth test led to a series of alterations in the D-21 design. In truth, the tests had been progressing positively until the accident and developers knew that only a few small scale changes were needed. 

First up was a change of mother. The B-52 Stratofortress would now be the aircraft of choice to launch the D-21 – seen as a more stable platform that the newer M-21. The second issue was how to get the D-21 up to speed substantially quicker. A solid-propellant rocket booster was added and at 14 metres (44 feet 4 inches) in length and weighing in at 6,000 kg (13,286 pounds) it was both bigger and heavier than the drone itself. The booster had a burn time of 87 seconds and produced a thrust of 27,300 pounds of force – roughly the same as one of the F-22 Raptor’s Pratt & Whitney F119-PW-100 engines – which was more than enough to carry the drone clear of the B-52.  

On 28th September 1967 a D-21B, as they were now known, was attached to a B-52 shortly before take-off. These B-52s had been modified to carry their new cargo on extra pylons added under each wing. The D-21Bs were then connected to each of these pylons from attachments points on the drones spine. 

No doubt there were high hopes as the fifth test began, but somewhat comically, the D-21B fell off the pylon in mid-air due to a damaged nut. Three more tests quickly followed, all of which were recorded as unsuccessful, but we’re not entirely sure why. With frustration mounting a full review was ordered before tests resumed, but the next 8 launches were a mixture of success and failure. On 16th June 1968, a D-21 finally completed a mission profile and its detached camera section was successfully retrieved but with two further failures, then a success, then two failures and lastly two successes, it hardly painted a picture of confidence.   

Operational History

With its checkered testing history, you might be surprised that it became fully active so quickly. In total, four missions were carried out using D-21Bs under the codename Senior Bowl and I’d love to be able to regale you with many successful missions, but alas it was not to be. 

If you’ve been wondering why the D-21 was scrapped so quickly, well here we go. The U.S was not quite ready to use this shaky drone over the Soviet Union, but the People’s Republic of China was something quite different. Their interest lay in the Lop Nor nuclear test site located in the far west of China where the country had detonated its first hydrogen bomb in 1967. 

The first mission began on 9th November 1969 but the D-21 failed to turn around and in fact carried on blindly before crashing in Soviet territory. The fate of this drone was a mystery for many years before it was revealed that the Soviets had recovered the wreckage in Siberia and had attempted to reverse engineer the technology. There was brief talk about a Soviet version of the D-21, known as the Voron, but for whatever reason, it never came to pass. 

The second flight was better but its camera hatch suffered a parachute malfunction and it was lost at sea. The third attempt also ended up in the ocean after it had been missed by the recovery aircraft. A destroyer was dispatched to recover the camera but ended up destroying it in the process as the ship sailed over it. The fourth, and final mission, also ended in disaster as the D-21 crashed in China’s Yunnan province, where it was recovered by local authorities. 

Cancellation

The brief, but eventful life of the D-21 came to an end on 23rd July 1971 when the program was cancelled – and with its poor track record, it must have been expected. A total of 38 D-21 or D-21Bs had been built, 21 of which had already been used up either through testing or on missions. The remaining drones eventually found their way to the Davis-Monthan Air Force Base near Tucson, Arizona – commonly known as “boneyard” as it acts as a final resting place for many disused aircraft. 

The tale of the D-21 is one that never even really got started. Before them, manned spy planes were seen as they answer, and during their bumpy career, the emergence of surveillance satellites meant that the D-21 filled a very short window of possibility – and let’s be very honest here, didn’t exactly do it very well. 

However – take a step back from the preposterously awful career record that the D-21 had and you’ll be amazed at what the U.S nearly pulled off over 50 years ago. This was a drone that travelled nearly 1,000 mp/h faster than Concorde and at a height that is approaching three times that of a conventional passenger airliner. Yes, it never actually worked in a real-life situation, but it came mightily close.  

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