How Did the SR-71 Blackbird Get Made and How was It So Fast?

On September 1, 1974, U.S. Air Force pilots Major James Sullivan and Major Joel Widdifield took off from New York City and headed East over the Atlantic Ocean. By the time they reached London, only one hour, 54 minutes, and 56 seconds had elapsed – less than 1/17th the time it had taken for Charles Lindbergh to make the same flight only 47 years before. This impressive feat – a world record which stands to this day – was made possible by the groundbreaking aircraft Sullivan and Widdifield were flying: the legendary Lockheed SR-71 Blackbird. In almost every sense, the sleek, alien-looking Blackbird was a flying superlative. Capable of traveling at more than three times the speed of sound at altitudes exceeding 27 kilometres – so fast it could even outrun air-to-air missiles – it remains the fastest military aircraft to see service and the fastest air-breathing aircraft ever built. But what mission was this space-age marvel designed for, and what allowed it to fly so blisteringly fast? Let’s find out as we dive into the incredible history and engineering of one of history’s most technologically-advanced aircraft.

The story of the Blackbird begins in 1958 with engineer Clarence “Kelly” Johnson, director of Lockheed Aircraft’s Advanced Design Projects Office – better known as “Skunk Works.” Formed in 1939 and named after the fictional “Skonk Works” moonshine distillery in Al Capp’s popular L’il Abner comic strip, Skunk Works quickly became known for its innovative and groundbreaking aircraft designs, including the P-38 Lightning long-range fighter and the P-80 Shooting Star, the United States’ first production military jet. In 1954, Skunk Works introduced two of its most iconic designs, which could not have been more different in concept: the F-104 Starfighter and the U-2 “Dragon Lady.” Nicknamed the “missile with a man in it”, the Starfighter had a narrow, needle-like fuselage, stubby razor-sharp wings and powerful General Electric J79 turbojet engine which allowed it to reach twice the speed of sound and climb to an altitude of 25,000 metres in only 4.5 minutes.

The U-2, by contrast, was a spy plane designed not for speed, but altitude. Essentially a jet-powered glider, U-2 had slender, 24-metre long wings that allowed it to cruise at altitudes in excess of 20,000 metres – well out of reach of Soviet air defences. However, this impressive performance comes at a cost. At these altitudes, the difference between stall speed (the speed at which insufficient air flows over the wings) and critical Mach number (the speed at which shock waves begin to form on the wings) – is measured in a handful of knots, meaning any sudden change in speed while climbing or descending can send the aircraft tumbling out of the sky. This precarious flight regime – known to pilots as the “coffin corner” – makes the U-2 one of the most difficult aircraft in the world to fly – and its pilots generally considered among the best in the world.

Operated by the CIA from bases in West Germany, Alaska, Japan, and Pakistan, U-2s began making regular overflights of Soviet territory in 1956, using powerful cameras to photograph air and naval bases, missile launching sites, weapons factories, and other strategic targets. U-2s revealed that the Soviets’ supposed superiority in strategic weapons – the so-called “bomber gap” and “missile gap” – was, in fact, a myth, and later uncovered the evidence that would kick off the 1962 Cuban Missile Crisis.

Initially, it was believed that Soviet radar was unable to track the U-2, but this assumption was soon proven false, and time and time again manned interceptors and guided missiles were dispatched – unsuccessfully – to shoot down the high-flying intruders. Various attempts were made to reduce the U-2’s radar cross-section, but these proved largely ineffective and greatly reduced the aircraft’s operating altitude – making it more vulnerable. With Soviet air defenses steadily improving, it was only a matter of time before the U-2 overflights became untenable. In response, in 1958 CIA officer Richard Bissell launched Project GUSTO, a committee chaired by Polaroid chairman Edwin Land and tasked with discussing possible high-performance successors to the U-2. Between November 1957 and August 1959, the committee met seven times, with several meetings being attended by representatives of major aircraft manufacturers including Lockheed’s Kelly Johnson. Of the next generation of strategic reconnaissance aircraft, Johnson declared:

“It makes no sense to just take this one or two steps ahead, because we’d be buying only a couple of years before the Russians would be able to nail us again….I want us to come up with an airplane that can rule the skies for a decade or more.”

According to Johnson, the new aircraft should be capable of cruising at speeds of 3-4 times the speed of sound and altitudes in excess of 30,000 metres. This would not only allow it to outrun and out-climb any manned interceptor or surface-to-air missile, but also avoid detection by exploiting a weakness of early radar systems known as the blip-to-scan ratio. In simple terms, if the aircraft could fly faster than the radar’s refresh rate, then it would register as background noise and be filtered out, rendering it all but invisible.

Starting in 1958, several manufacturers began submitting proposals for such an aircraft, which ran the gamut from the merely ambitious to the truly exotic. For example, the U.S. Navy proposed a Mach-4 capable aircraft powered by ramjets and launched from a nuclear submarine. Ramjets, which have no moving parts, are efficient at high speeds but depend on forward motion to function and cannot accelerate from a standstill. The Navy’s design was thus lifted into the air by a giant helium balloon and accelerated to cruising speed by rocket boosters. However, when Lockheed’s Kelly Johnson analyzed the design and discovered that the balloon would have to be nearly two kilometres in diameter, the Navy withdrew its proposal.

Convair’s proposal, known as the First Invisible Super Hustler or FISH, was only slightly less ambitious. Powered by two ramjets and capable of cruising at Mach 4, FISH was a parasite aircraft designed to be launched from an enlarged version of Convair’s supersonic B-58 Hustler bomber. To withstand the enormous frictional heating encountered at high-supersonic speeds, the nose and wing leading edges were made of a special material developed by the Corning Glass Works called pyroceram.

Slightly more exotic was Lockheed’s initial proposal, the CL-400 Suntan. Resembling an enlarged F-104 Starfighter, Suntan was powered by a pair of wingtip-mounted ramjet engines burning pure liquid hydrogen. The hydrogen, stored in fuselage tanks, travelled to the engines though pipes in the leading edges of the wings, simultaneously pre-heating the fuel and cooling the airframe.

However, the GUSTO committee was unimpressed by these initial proposals and asked the competitors to re-submit designs based around the Pratt & Whitney J58 turbojet engine, developed in 1958 for use in various aircraft projects which never came to fruition. Lockheed’s new design, codenamed Archangel, was still ramjet-powered but used conventional fuel and was boosted to cruising speed by J58 engines running at full afterburner. Meanwhile, Convair’s resubmission, the Kingfish, was no longer air-launched but had a top speed of Mach 3.2 and a range of nearly 6,300 kilometres. Though the GUSTO committee liked Lockheed’s design, they felt that its radar cross-section was too high. This prompted Kelly Johnson to draft progressively improved versions of the design, culminating in A-11, which reduced the original cross-section by 90%. Finally, on August 28, 1959, the government declared Lockheed the winner of the new spy plane contract. The decision was based not only on the aircraft’s estimated performance, but also Lockheed’s track record of delivering “black projects” on-time, and under budget. By contrast, Convair had a long history of budget overruns and no secret projects division to rival Lockheed’s Skunk Works. In January 1960, the CIA placed a $96 million order for twelve A-11s, which in a sly bit of tongue-in-cheek naming were given the official codename of OXCART.

This decision could not have come at a better time, for just four months later the day the United States military had been dreading finally arrived. On May 1, 1960, CIA U-2 pilot Francis Gary Powers took off from Peshawar, Pakistan and turned northwest towards the Soviet border. Powers’s mission called for him to fly around 6,000 kilometres over Soviet territory, photographing a variety of targets including the Baikonur and Plesetsk cosmodromes and the Chelyabinsk-65 plutonium production plant before landing in Bodø, Norway. At first the flight was uneventful, with the Soviets trying but failing to intercept Powers using conventional jet fighters. However, soon after passing Chelyabinsk, he was finally shot down by an S-75 Dvina surface-to-air missile near the city of Sverdlovsk. Powers managed to bail out and parachute to the ground, whereupon he was captured and paraded before the world by the Soviet authorities. The U-2 incident of 1960 caused an international scandal, significantly setting back U.S.-Soviet relations. It also marked the end of American overflights of Soviet Territory, creating a severe intelligence blackout regarding Soviet military capabilities. At the time, Lockheed was well into development of its CORONA series of spy satellites, but this technology would not be ready for another year.

Meanwhile, Skunk Works pushed on with the development of the A-12. The challenge facing Kelly Johnson’s engineers was enormous, forcing them to rethink nearly every aspect of aircraft design. As Johnson would later state:

“Everything had to be invented. Everything.”

The conditions under which the A-11 was to operate were extreme: at three times the speed of sound, friction with the atmosphere would produce skin temperatures in excess of 500 degrees Celsius – temperatures that would melt a conventional aluminium airframe. It was thus decided to build 93% of the A-11 out of titanium, which is not only twice as dense as aluminium but far more heat-resistant. But, there was a tiny problem: in the late 1950s titanium was a scarce commodity, and the world’s largest source of the metal was…you guessed it: the Soviet Union. But while the CIA managed to get its hands on large quantities of Russian titanium through a network of dummy companies, buying only the high-grade metal that Lockheed needed risked tipping the Soviets off as to its ultimate use. Thus, the CIA was forced to import hundreds of tons of mixed-grade titanium, only around 7% of which was selected by Lockheed for use.

But the challenges didn’t end there, for titanium is a fiendishly difficult material to work with. Ordinary cadmium-laced tools embrittled the metal on contact and caused it to shatter, so new ones had to be manufactured from titanium. One one occasion when bolts and other fasteners began failing without apparent cause, it was discovered that all the wrenches in the factory also contained cadmium, forcing every tool box to be scoured for the offending tools. And then there were the welds, which seemed to crack almost at random. Further investigation revealed a bizarre pattern: welds made during the winter behaved normally, while those made during the summer tended to fail prematurely. After months of dogged detective work, the cause was finally traced to the water supply in Burbank, California, where the Lockheed factory was located. During the summer, the city added more chlorine to the water to prevented algae growth; when newly-welded titanium parts were washed in this extra-chlorinated water, it weakened the welds. When Johnson ordered the welds washed in distilled water instead, the problem disappeared.

But no sooner had Lockheed mastered the art of manufacturing titanium than did another, equally vexing problem appear. Frictional heating at high speeds caused the aircraft’s skin panels to expand and buckle, destroying the airframe. To counter this, Lockheed engineers replaced the flat panels with finely corrugated ones, allowing them to expand without buckling. Some engineers likened this technique to trying to get a 1930s-era Ford Trimotor or Junkers 52 – famous for their corrugated skin panels – to fly supersonically. In addition, the panels were also made undersize, so that their edges would only fit flush against each other once they had heated up. For weight-saving reasons, the outer skin also served as the walls of the fuel tanks, resulting in an alarming design quirk: sitting on the tarmac, the aircraft leaked fuel like a sieve. In operational use, standard procedure was to fill the tanks with just enough fuel to take off, whereupon the aircraft would rendezvous with an aerial refuelling tanker and top off its tanks. On reaching operational speed and altitude, thermal expansion caused the skin panels to expand and seal themselves, preventing further fuel leaks.

As can be imagined, leaking fuel all over the tarmac posed just a bit of a fire hazard, so a special high-flashpoint fuel called JP-7 was developed which could not be ignited by a stray flame or spark. However, since JP-7 could also not be lit by conventional jet engine ignitors, Lockheed developed a system to inject diborane, a pyrophoric gas that ignites spontaneously on contact with air, into the engines to ignite the stubborn fuel. The engines themselves were spun up prior to takeoff a special starter cart containing two Chevrolet big block engines putting out 600 horsepower.

The extreme temperatures encountered at Mach 3 required nearly every system in the aircraft to be specially engineered. Special lubricants and hydraulic fluids were developed that could withstand temperatures of up to 350 degrees Celsius, while the fuel system was designed to circulate JP-7 past particularly hot areas of the airframe in order to cool them. Control cables were made of a heat-stable steel-chromium-nickel alloy called Elgiloy – normally used in clock and watch springs – while all electrical connections were even plated in gold, which retains its conductivity better at higher temperatures than other metals. Due to weight restrictions the cockpit could not be insulated, forcing pilots to wear special air-conditioned pressure suits which also protected them against the near-vacuum of the upper stratosphere. Indeed, under cruising conditions the inside of the cockpit got so hot that during missions crews often heated up their meals by holding them up against the cockpit glass.

As specified by the GUSTO committee, the A-11 was powered by a pair of Pratt & Whitney J58 turbojet engines, which had to be extensively modified in order to operate reliably at full continuous afterburner and withstand the extreme conditions of Mach 3 flight. According to one Pratt & Whitney engineer:

“I do not know of a single part, down to the last cotter key, that could be made from the same materials as used on previous engines.”

The engines themselves were housed in streamlined wing-mounted nacelles which, at cruising speed, acted partially like ramjet engines, diverting a large proportion of the incoming air into the annular space between the engine and nacelle. As jet engines cannot ingest air travelling at supersonic speeds without flaming out, the nacelle inlets were fitted with special cone-shaped structures that generated shock waves and slowed the incoming air to subsonic speeds before it entered the engines.

But no matter how fast the A-11 flew, it would be useless as a reconnaissance aircraft if it could not take clear pictures. Thus, considerable engineering attention was devoted to the fused-quartz window for the onboard camera. Due to the 500-degree difference in temperature between the inside and the outside of the aircraft, this window was susceptible to optical distortion that could potentially ruin any photos taken through it. This problem caused considerable anxiety for the design team until Corning Glassworks developed an innovative method for fusing the glass to its titanium frame using powerful high-frequency sound waves. The camera itself, manufactured by Perkin-Elmer, carried 1500 metres of film and could photograph a 113 kilometre-wide swath of land from an altitude of 30,000 metres with a resolution of 30 centimetres.

In November 1959, long before production of the first prototypes had begun, Lockheed built a full-sized mockup of the A-11 and shipped it to Groom Lake, Nevada – better known as Area 51 – where it was mounted on a pylon and bombarded with radar waves from various angles. These tests revealed that the aircraft’s radar cross-section was still unacceptably high, forcing Lockheed to make further modifications to the design. These included replacing the leading edges of the wings and tail fins with a radar-absorbing composite material made of iron oxide, silicon, and asbestos; and blending the fuselage and wings together with sharp, fin-like structures known as chines, giving the aircraft an otherworldly appearance which aviation historian Peter Merlin once described as:

“…more organic than mechanical. Most conventional airplanes look like someone built them – this one almost looks like it was grown.”

It was later discovered that in addition to deflecting radar, the chines had the added benefit of generating additional lift at supersonic speeds. In light of these modifications, the aircraft’s designation was changed from A-11 to A-12 – which it would maintain going forward.

Overcoming all these unprecedented technical difficulties proved extremely expensive and time-consuming. Delivery of the first prototype was originally promised for May 1961, but as development dragged on this was moved to August and the maiden flight to December. Meanwhile, the $96 million budget had ballooned to over $161 million. Richard Bissell – then embroiled in the fallout from the Bay of Pigs debacle, wrote a frantic letter to Kelly Johnson, stating:

“I have learned of your expected additional delay in first flight from 30 August to 1 December 1961. This news is extremely shocking on top of our previous slippage from May to August and my understanding as of our meeting 19 December that the titanium extrusion problems were essentially overcome. I trust this is the last of such disappointments short of a severe earthquake in Burbank.”

But to Bissell’s dismay, the problems just kept coming. Due to the hyper-advanced materials and manufacturing techniques involved, the A-12 could not be mass-produced like a regular aircraft; each airframe was essentially a hand-crafted work of art. In July 1961, Johnson wrote in his log that he was:

“…having a horrible time building the first airplane …everyone on edge…and we still have a long, long way to go.”

In an attempt to rein in costs and get the project back on track, the CIA reduced its order from 12 to 10 aircraft and dispatched one of its own aerospace engineers to Lockheed to supervise final assembly. Meanwhile, Pratt & Whitney was also having serious problems getting the J58 engine up to Lockheed’s specifications. To prevent further delays, it was decided to carry out the first test flights using the less powerful J75 engine used in the U-2. This would theoretically allow the A-12 to reach altitudes of 15,000 metres and speed of up to Mach 1.6.

Meanwhile, the CIA was searching for the men who would eventually fly the A-12. The selection requirements were nearly as strict as those used to choose America’s first astronauts, the Mercury Seven: candidates had to be qualified to fly high-performance jet aircraft, be 25-40 years old, and be under 6 feet tall and under 175 pounds to fit into the A-12’s cockpit. They also had to pass a gruelling battery of medical examinations as well as interviews intended to gauge their political reliability and emotional stability. By November 1961, a preliminary batch of 12 pilots had been selected: William Skliar, Lon Walter, Ronald “Jack” Layton, Francis Murray, Kenneth Collins, Mele Vojvodich Jr., Dennis Sullivan, Walter Ray, Jack Weeks, David Young, and Russell Scott. Like their predecessors who flew the U-2, these men officially resigned from the military to become contract employees of the CIA, with the understanding that they could later return to active service with no loss of rank or seniority – a practice known as “sheep dipping.”

Finally, on February 28, 1962, the first prototype A-12 was packed into two large crates and shipped by road from Skunk Works in Burbank to Groom Lake for flight testing. As no self-respecting pilot would fly something with a name as unsexy as “oxcart”, the test pilots dubbed the exotic new aircraft “Cygnus” after the stellar constellation. On April 24, Lockheed test pilot Lou Schalk was performing high-speed taxi tests when the A-12 accidentally became airborne for several seconds, making its first – albeit brief – flight. The next day, the A-12 made its first proper – though still unofficial – flight, with Schalk once again at the controls. Barely 20 seconds after takeoff the aircraft began to oscillate violently; rather than circle around to land, Schalk opted to set the aircraft down on the dry lake bed beyond the end of the runway. As the A-12 came to a halt, Schalk heard the angry voice of Kelly Johnson growling over the radio: “What the hell, Lou?”

The next day Schalk took off on another unofficial test flight, keeping the landing gear extended in case he once again needed to put down quickly. At first the flight went perfectly, but soon the aircraft began shedding titanium fillets from the wing leading edges. It took Lockheed technicians days to comb the dry lake bed for the pieces and fit them back onto the aircraft. Nonetheless, Johnson was pleased with the results, stating:

“We showed that the first flight troubles were not caused by basic aircraft [in]stability.” 

Finally, on April 30, the A-12 made its first official flight in front of Air Force and CIA representatives – one year later than originally planned.

From here flight testing carried on at a steady pace, with the first A-12 being joined by a second in June 1962. On May 2, the A-12 broke the sound barrier for the first time, achieving a top speed of Mach 1.1. However, without proper engines, the A-12 would never be able to reach its full potential. The CIA thus placed additional pressure on Pratt & Whitney to deliver, and in January 1963 the first J58-powered A-12s finally took to the air. Meanwhile, world events clearly demonstrated the urgent need for an aircraft like the A-12. On October 27, 1962, U-2 pilot Rudolph Anderson was shot down and killed while photographing Soviet ballistic missile installations in Cuba. In the wake of this incident, the A-12 program shifted into high gear, with Lou Schalk performing the first Mach 3 flight on July 20, 1963. By 1966, A-12s were regularly smashing aviation records – albeit secretly and unofficially. For example, on December 21 Lockheed test pilot Bill Park flew his aircraft on a course that took him from Groom Lake northward over Yellowstone National Park to Bismarck, North Dakota; then east to Duluth, Minnesota; south to Atlanta and Tampa; northwest to Portland; and finally southwest around Knoxville and Memphis before returning to Nevada – a total distance of 16,300 kilometres in only six hours.

For training purposes, one of the A-12s was fitted with a second cockpit for an instructor. Nicknamed “the Titanium Goose”, the trainer used the less-powerful J75 engines, saving the scarcer and more expensive J58s for the operational aircraft. And while initially the A-12s sported a bare-titanium finish, in 1964 they were coated with the now-iconic dark black radiative paint to allow heat to more easily dissipate.

While flight tests revealed Kelly Johnson’s titanium wonder to be a basically sound design, it was still a tricky and sometimes dangerous aircraft to fly. The first loss of an A-12 occurred on May 24, 1963 when pilot Ken Collins lost the use of his instruments and was forced to eject near Wendover, Utah. Collins was unhurt and the wreckage was quickly gathered up and spirited away, with locals who witnessed the crash being made to sign non-disclosure agreements. The cause of the crash was soon traced to icing in the pitot tube – and for more on the absolutely insane number of crashes caused by this very same problem, please check out our previous video How a Tiny Hole Caused Dozens of Air Disasters.

One persistent problem encountered during flight testing was the tendency for the shock waves formed by the engine intake cones to become detached, starving the engines of fuel and causing a violent deceleration that pilots likened to “being caught in a train crash.” This problem threatened to derail the entire project, and it was months before engineers perfected a system that could automatically move the intake cones and “recapture” the shock waves in a fraction of a second.

In total, the A-12s would make 2,850 test flights at Groom Lake before the type became operational, with three more airframes being lost in the process. The first loss occurred on July 9, 1964 when a pitch-control servo froze and the aircraft became uncontrollable. Pilot Bill Park ejected safely. The second occurred on December 28, 1965, when pilot Mele Vojvodich experienced a series of violent yawing and pitching motions shortly after takeoff and was forced to eject. The cause of the crash was later traced to the gyroscopes in the stability-augmentation system, which had been incorrectly wired by a maintenance technician. Finally, on January 5, 1967 an A-12 ran out of fuel and crashed on approach to the Groom Lake runway. Pilot Walter Ray ejected successfully, but the seat failed to separate and he was killed on impact with the ground – the first fatality of the A-12 program. No definite cause for the crash was ever determined, but investigators suspected a fault in the fuel quantity indication system.

While designed from the get-go as an unarmed reconnaissance platform, the A-12’s blistering performance prompted many to imagine alternative roles for the aircraft. For example, General Curtis LeMay, mead of Strategic Air Command, considered using the A-12 as a high-speed nuclear bomber for striking targets deep behind enemy lines; while the regular Air Force brass envisioned both a high-speed, high-altitude interceptor for shooting down Russian strategic bombers and a larger, longer-range reconnaissance aircraft for evaluating target damage following a nuclear strike. But while LeMay’s bomber was never built, the two Air Force variants were. The interceptor, designated the YF-12, was fitted with a second cockpit for a Weapons System Officer, an AN/ASG-18 Fire Control System, and an armament of AIM-47A Falcon air-to-air missiles, with the front of the fuselage chines being cut away to accommodate the targeting radome. Three prototype YF-12s were produced, with the type making its maiden flight on August 7, 1963.

The second Air Force variant, designated RS-71 for “Reconnaissance/Strike”, was effectively a larger and more sophisticated version of the A-12. It measured a full metre longer and weighted 6,800 kilograms more, had a 13% greater range, and was fitted with a second cockpit for a Reconnaissance Systems Officer as well as additional photographic, synthetic aperture radar, and electronic intelligence or ELINT sensors. First flown on December 22, 1964, the RS-71 was coated in the same radiative black paint as the A-12, earning it the immortal nickname of “Blackbird.”

Another project to grow out of the A-12 programme was the Lockheed D-21, an autonomous ramjet-powered drone designed to penetrate deep into enemy territory. Built using many of the same materials and techniques as the A-12 and RS-71, the D-21 was designed to be launched from the back of a specially-modified A-12 mothership known as the M-21. Once launched, the D-21 would streak over enemy territory at a speed of Mach 3.3 and altitude of 29,000 metres, using an inertial guidance system to navigate and a sophisticated camera system to photograph enemy targets. It would then fly over international waters and release its film canister on a parachute, which would be snatched out of the air by a Lockheed C-130 transport aircraft. Though today this might sound needlessly complicated, this procedure had already been perfected for recovering film canisters from CORONA spy satellites and was remarkably effective.

Two A-12s were converted into M-21 motherships, with flight tests beginning in March 1966. The first three test flights returned mixed results, with the D-21s suffering various systems failures. The drone also demonstrated an unnerving tendency to “float” in place above the mothership’s fuselage for several seconds after launch. For this reason, launches were conducted while performing an outside loop to help the drone separate from the mothership. The testing program came to an abrupt halt on July 30, 1966 when the D-21 suffered an engine failure immediately after launch and struck the mothership’s tail, destroying both aircraft and forcing the M-21 crew to eject. Pilot Bill Park survived, but Launch Control Officer Ray Torrick accidentally opened his helmet visor upon parachuting into the ocean, causing his suit to fill with water and drag him under. Following this disaster, M-21 launches were abandoned and the D-21 was instead modified to be launched from the wing of a Boeing B-52 Stratofortress strategic bomber, the drone being accelerated to cruise speed by a solid rocket booster. This configuration proved much safer, and in November 1969 the Air Force launched Operation Senior Bowl, an attempt to use B-52 – launched D-21s to spy on the Chinese nuclear test site at Lop Nor. Between November 9, 1969 and March 20, 1971, six Senior Bowl missions were flown – with disappointing results. Two drones failed to reach their targets and crashed, two successfully released their film canisters only for them to be lost at sea, while two canisters were successfully recovered. However, most of the photographs were ruined due to improper film processing techniques. In July 1971, the D-21 project was finally cancelled.

Throughout the development of the A-12 and its derivatives, the U.S. government faced an increasingly troubling question: how long could the project remain secret? Spiralling costs made it increasingly difficult for the Department of Defense to deny the A-12’s existence, while airline pilots and other witnesses regularly spotted the mysterious aircraft on test and training flights over the southwestern United States. Despite the efforts of Lockheed, the CIA, and the Air Force to keep the project under wraps, sooner or later the truth was bound to get out. Furthermore, Lockheed knew that its cutting-edge research on supersonic aerodynamics would be of great interest to the aviation industry, especially for the design of the Supersonic Transport or SST – the doomed American predecessor to the legendary Concorde. In the end a clever plan was hatched to manage the information that reached the public, and on February 24, 1964, President Lyndon B. Johnson announced to the nation:

“The United States has successfully developed an advanced experimental jet aircraft, the A-11, which has been tested in sustained flight at more than 2,000 mph and at altitudes in excess of 70,000 feet. The performance of the A-11 far exceeds that of any other aircraft in the world today. The development of this aircraft has been made possible by major advances in aircraft technology of great significance to both military and commercial applications. Several A-11 aircraft are now being flight tested at Edwards AFB in California… The A-11 aircraft now at Edwards AFB are undergoing extensive tests to determine their capabilities as long-range interceptors.”

Five months later Johnson spoke again, announcing:

“…the successful development of a major new strategic manned aircraft system, which will be employed by the Strategic Air Command. This system employs the new SR-71 aircraft, and provides a long-range, advanced strategic reconnaissance plane for military use, capable of worldwide reconnaissance for military operations… The SR-71 aircraft reconnaissance system is the most advanced in the world. The aircraft will fly at more than three time the speed of sound. It will operate at altitudes in excess of 80,000 feet. It will use the most advanced observation equipment of all kinds in the world. The aircraft will provide the strategic forces of the United States with an outstanding long-range reconnaissance capability. The system will be used during periods of military hostilities and in other situations in which the United States military forces may be confronting foreign military forces.”

Johnson’s choice of words was very deliberate. For instance, the use of A-11 – the A-12’s original designation before receiving its radar-evading modification – was a misdirect meant to throw off potential spies. Furthermore, by publicly acknowledging the existence of the very similar-looking YF-12 interceptor, it was hoped that the original A-12 reconnaissance aircraft could be kept in the shadows. For a time, the ploy seemed to work, with dozens of aviation journals and other publications writing exhaustive articles on the hyper-advanced “A-11” based on what little technical information the government chose to declassify. Meanwhile, the A-12 testing and training program carried on in relative obscurity.

However, the deception also had unexpected consequences. At the time President Johnson made his first announcement in February, there were no YF-12s at Edwards Air Force Base. Caught by surprise, the Air Force hastily flew two of the prototypes to Edwards to back up the President’s story. So rushed was this operation that when the aircraft were rolled into the hangar, the heat from their fuselages set off the sprinkler system, soaking the welcoming committee.

Johnson’s second speech also had an unexpected legacy. Though the official designation of the Air Force’s A-12 derivative was RS-71, Johnson mispronounced it as SR-71. The Air Force decided it was easier to redesignate the aircraft than publicly correct the President, and so the SR-71 it became.

In 1967 – a full 5 years after its maiden flight – the A-12 finally reached operational status. However, by this time, the mission it had been designed for had disappeared. Following the shoot-downs of Francis Gary Powers in 1960 and Rudolph Anderson in 1962, the U.S. government abandoned manned overflights of Soviet and Cuban territory as too politically risky. This mission instead fell to the CORONA spy satellites, which by 1967 were regularly returning high-quality photographic intelligence. The A-12 was thus repurposed as a tactical reconnaissance platform for gathering up-to-the-minute intelligence in active war zones – such as the conflict then raging in Vietnam.

In 1967, the U.S. military was concerned by reports that North Vietnam had obtained from the Soviet Union large numbers of medium-range surface-to-surface missiles with which to attack the south. In response, the CIA launched Operation Black Shield to evaluate the North’s missile capabilities. In May 1967, three A-12s flew from Groom lake to Kadena Air Force Base in Okinawa, Japan, crossing the Pacific in an incredible 5 hours and 55 minutes. The unit was declared operational on May 30, and the following day pilot Mele Vojvodich flew the first operational Black Shield mission, flying at Mach 3.1 at an altitude of 24,000 metres and capturing a nearly 2-kilometre-long film strip covering most of North Vietnam and the Demilitarized Zone between the North and South. To the enormous relief of the Pentagon, this and subsequent missions revealed that the North did not, in fact, have any surface-to-surface missiles.

Over the next 7 months the A-12s would carry out 22 Black Shield sorties, photographing artillery batteries, factories, supply depots, harbours, radar installations, prisoner of war camps, and other strategic sites. This intelligence proved key to President Johnson’s decision to approve large-scale air raids over North Vietnam. Yet despite their advanced stealth features, the aircraft were regularly detected and tracked by North Vietnamese search radar. Radar technology had improved significantly since the A-12 was designed, making many of its advanced stealth features of limited value. On October 28, an A-12 was fired upon for the first time, but the missile failed to lock in on its target. Two days later over Hanoi, pilot Denny Sullivan had a much closer call when a North Vietnamese SAM site launched no fewer than six missiles at him. As he later recalled:

“Here comes a big’ol telephone sailing right by the cockpit—going straight up. That’s interesting . . . So I continued down the route, and didn’t see anything—until I got down the road, and then I could see behind me in the rear-view periscope at least four missile contrails, all spread out. Those four contrails went up about 90-95,000 feet and all turned over, bunched up in a line, headed for my tail end. I said, ‘Holy smokes—those things fly pretty good up there for something which doesn’t have much in the way of wings.’ So I watched them come.… They’d get up right behind me, very close, and all of the sudden there’d be a big red fireball—a big white cloud of smoke—and you’d immediately pull away from it. You were going [41 miles] a minute. Every one of those SAMs guided absolutely perfectly and did the same darn thing.”

While the A-12 had a maximum speed of Mach 3.2, the Soviet-built S-75 Dvina surface-to-air missile could reach Mach 3.5. Nonetheless, Sullivan successfully evaded the barrage and made it safely back to Kadena. Back at base, maintenance crews discovered a fragment of one of the missiles lodged in the wing near one of the fuel tanks. It was the first and only time an A-12 would suffer weapons damage in combat.

On January 23, 1968, a North Korean torpedo boat attacked and captured the USS Pueblo, a U.S. Navy spy ship operating in international waters. Fearing that this incident was a prelude to a much larger attack, three days later the CIA dispatched an A-12 flown by Jack Weeks on a reconnaissance mission over North Korea. This and a subsequent flight revealed that Pyongyang had not, in fact, mobilized its forces for war. As a result, President Johnson scrapped plans for a punitive counter-strike against North Korea and took a more diplomatic approach to the crisis, one which saw the crew of the Pueblo released less than a year later. Meanwhile, five more Black Shield missions were flown over North Vietnam and Cambodia.

But just as it was beginning to prove its usefulness, the A-12’s operational career came to an abrupt halt. With its defence budget stretched to the breaking point by the ongoing Vietnam War, the U.S. government could no longer afford to fund three very similar aircraft programs: the A-12, the YF-12, and the SR-71.

As improving relations with the Soviet Union made North American aerospace defence less of a priority, the YF-12 program was cancelled, while in November 1967, the Air Force staged Operation Nice Girl, an official fly-off between the A-12 and SR-71 to determine which was the superior reconnaissance aircraft. Over the course of three days, the two competing aircraft were made to fly identical routes stretching from California to Louisiana and back, taking off one hour apart and performing various tasks including photographing designated targets and performing aerial refuelling. The results were inconclusive, but due to its more sophisticated sensor suite and longer range, the SR-71 was ultimately declared the winner. Other factors may also have played into this decision, for it was widely known that the Air Force was jealous of the CIA’s A-12 program and wanted to keep high-speed military aviation all to itself. Whatever the case, after only 10 months of operational service, the A-12 was retired and all further Black Shield missions flown by SR-71s. Of the 15 A-12s produced, three flew a total of 29 Black Shield missions over southeast Asia while six were lost to accidents with three pilot fatalities. The remaining nine aircraft were placed in storage in Palmdale, California, where they remained top-secret for nearly 20 years. After the A-12 project was finally declassified in 1981, the aircraft were taken out of storage and disbursed to various museums across the United States, where they remain to this day.

But while the A-12 languished in obscurity, the SR-71 quickly became one of the most famous aircraft in the world, smashing dozens of aviation records. For example, on July 28, 1976, Captain Robert Helt broke the world absolute altitude record by reaching a height of 26,929 metres. That same day, another SR-71 broke the absolute airspeed record at 3.529 kilometres per hour – approximately Mach 3.3. Two years earlier on September 1, 1974, pilot James Sullivan and RSO Noel Widdifield flew from New York to London – a distance of 5,570 kilometres – in just one hour, 54 minutes, and 56 seconds – achieving an average speed of 2,908 kilometres an hour or around Mach 2.72. And three years before that on April 26, 1971, pilot Thomas Estes and RSO Dewain Vick flew a distance of 24,000 kilometres in just 10 hours and 30 minutes. This flight earned the pair the 1971 Mackay Trophy for “the most meritorious flight of the year” and the 1972 Harmon Trophy for “the most outstanding international achievement in the art/science of aeronautics.”

It is important to note here that while other aircraft have flown faster and higher, these feats were achieved under very special circumstances. For example, on August 22, 1963 pilot Joseph Walker reached a record altitude of 108 kilometres – past the official edge of space – while on October 3, 1967, William “Pete” Knight reached a record speed or 7,274 kilometres an hour or Mach 6.7. However, both pilots were flying the North American X-15, a rocket-powered research plane carried aloft and launched at altitude from a larger carrier aircraft. Pilots flying conventional jets have also reached altitudes as high as 35,230 metres by performing high-speed “zoom climbs.” By contrast, the SR-71 set all its records in level, sustained flight using air-breathing engines after taking off from the ground under its own power. And while the SR-71’s predecessor, the A-12, could technically fly slightly higher and faster, it remained classified throughout its operational career and was thus ineligible to compete for international aviation records. Similarly, while SR-71 pilot Brian Shul claims that on April 15, 1986 he achieved a speed of Mach 3.5 in order to evade a surface-to-air-missile over Libya, this record has never been confirmed over a standard closed course and thus remains unofficial. For these reasons, the SR-71 is officially recognized as the fastest and highest-flying air-breathing aircraft ever built, with the records set in the 1970s still standing to this day.

But the SR-71 did far more than just break records and turn heads at airshows. Since entering service in 1966, the Blackbird participated in dozens of armed conflicts around the world, collecting vital intelligence during the 1973 Yom Kippur War, the Israeli invasion of Lebanon, and the 1986 U.S. airstrikes in Libya. Between 1977 and 1988, SR-71s based at RAF Mildenhall in England flew 322 so-called “Baltic Express” missions along the northern coast of the Soviet Union and East Germany – often violating Swedish airspace in the process. The Swedes responded by scrambling supersonic fighters to defend their neutrality, but the SR-71s were so much faster than these interceptors that none were ever successfully engaged. Ever adaptable, the SR-71 was even used domestically in 1971 as part of the FBI’s manhunt for mysterious skyjacker D.B. Cooper.

All operational SR-71s were flown by the 9^th Strategic Reconnaissance Wing, based at Beale Air Force Base in California but deployed from various Operating Locations or OLs including Eilson Air Force Base, Alaska; RAF Mildenhall; Diego Garcia in the Indian Ocean; and Kadena Air Force Base in Okinawa, where the SR-71 acquired its second major nickname: Habu. This was a reference to an indigenous species of venomous snake the aircraft was thought to resemble. Piloting the SR-71 was a very exclusive club, with only 93 Air Force pilots total qualifying as “sled drivers”. This exclusivity was very much warranted, for like its predecessors the SR-71 was a very difficult – and often dangerous – aircraft to fly. Of the 32 airframes built, none were ever lost to enemy action, but 12 were destroyed in various accidents. However, only one crewman ever lost his life while flying the Blackbird: Lockheed test navigation and systems specialist Jim Zwayer, whose aircraft broke up in midair during a test flight on January 25, 1966. While pilot Bill Weaver miraculously survived the breakup and safely parachuted to earth, Zwayer’s neck was broken, killing him instantly.

By the end of the 1980s, SR-71s had flown more than 3,000 sorties and accumulated more than 11,000 operational flight hours – more than a quarter of these spent at Mach 3. Yet just like with the A-12 before it, just as the SR-71 was beginning to hit its stride, the decision was made to retire it. The official reason was largely budgetary. The SR-71 was an extremely complex and expensive aircraft to operate, requiring a large army of support staff and a global network of air bases, refueling aircraft, and other infrastructure. Indeed, then-Secretary of Defense Dick Cheney estimated that the SR-71 cost a whopping $85,000 a minute to fly, while the whole project absorbed some $300 million per year. Meanwhile, detractors argued, the same job could be done more cheaply – and more effectively – by sophisticated spy satellites, unmanned aerial vehicles or UAVs, and – ironically – the very aircraft the SR-71 had been designed to replace: the Lockheed U-2. For despite being superior to the U-2 in nearly every way, the SR-71 had one major shortcoming: its lack of a data link system, which prevented the intelligence collected from being transmitted and used in real-time. Meanwhile, the U-2 had been upgraded with such a system, making it a more capable tactical reconnaissance platform despite its greater vulnerability to anti-aircraft defenses. While proponents argued that the SR-71 provided unique capabilities that other reconnaissance platforms could not, the aircraft was finally retired in October 1989. As with the A-12, part of the decision may also have been political, with the Air Force using the cancellation of the SR-71 project a bargaining chip to secure funding for higher-priority projects like the Boeing B-2 Spirit “Stealth Bomber.”

The timing of the decision proved an inauspicious one, as the tactical reconnaissance capability provided by the SR-71 was sorely missed by Coalition forces during the 1991 Persian Gulf War. This, along with similar intelligence-gathering difficulties during the Bosnian War of 1992-1995, prompted a re-evaluation of the SR-71. As no technology existed which could match the Blackbird’s capabilities, Congress agreed to allocate $72 million to re-activate three aircraft – which were fitted with real-time data links to bring them up to modern standards.

However, this reprieve proved short-lived. The Air Force had not budgeted for the SR-71’s reactivation, and feared that this decision would divert funds from other, more important projects. Yet despite attempts by the Air Force to shut down the program, Congress nonetheless re-approved the allotted funding. In October 1997, President Bill Clinton attempted to use the line-item veto to cancel the allocation, but this was quickly struck down by the Supreme Court as unconstitutional. The status of the SR-71 thus remained up in the air… until September 1998, when the Air Force finally redistributed the reactivation funds and retired the aircraft for good.

But this was not the end of the Blackbird’s story, for two examples were sent to NASA for use as hypersonic testbeds. Among other things, the two Blackbirds were used to test parts of the aerospike rocket engine for the Lockheed Martin X-33, a proposed reusable, single-stage-to-orbit spaceplane. The last SR-71 flights took place in 1999, whereupon the surviving aircraft were decommissioned and sent off for display in aviation museums. It was the end of an era. To this day, no manned conventional aircraft has ever flown as fast or as high.

Today, the role of the Blackbird is increasingly being taken over by unmanned aerial vehicles or drones, which can be deployed faster and loiter over a target longer without risking the life of a pilot. However, no drones in use today can match the Blackbird’s incredible speed – speed which allowed it to outrun every adversary – even missiles – for nearly three decades. But this may be about to change, as Lockheed is currently developing an unmanned successor called the SR-72 or “son of Blackbird” whose supersonic combustion ramjet or Scramjet engines will allow it to cruise at six times the speed of sound – twice as fast as its manned predecessor. The SR-72 is expected to enter service sometime in the 2030s.

And while the Blackbird no longer graces the skies, its influence is still being felt to this day. Many of the aerodynamic and radar-evading technologies developed for the SR-71 and its predecessor the A-12 were incorporated into the design of other aircraft, such as the supersonic Concorde airliner and modern stealth aircraft like the F-117 Nighthawk, F-22 Raptor, and F-35 Lightning II. The Blackbird’s distinct profile also served as the inspiration for the X-jet used by the Marvel superhero team the X-Men. That this design is still being used in the current-day movies is a testament to the cutting-edge vision of Kelly Johnson and Lockheed’s Skunk works. For despite being designed in the late 1950s, the Blackbird still looks like something out of the distant future.

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