“Faster than a speeding bullet” may bring to mind a certain superhero from the planet Krypton, but it was literally true of the SR-71 Blackbird, the sleek, stealthy Air Force spy plane taken up for its first test flight 50 years ago on December 22, 1964. Created by Lockheed’s legendary Skunk Works team—a top-secret crew of techno wizards—at the height of the cold war, the Blackbird cruised at more than three times the speed of sound. That translates to better than 2,000 miles per hour—at altitudes between 75,000 and 85,000 feet, too high and too fast to be shot down by an enemy fighter or a surface-to-air missile.

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Expensive to maintain and fly, the SR-71 was retired from the Air Force in 1990. Blackbird number 972, which set four international speed records that year, now is on display at the Smithsonian National Air and Space Museum Udvar-Hazy Center in Chantilly, Virginia. Standing before the aircraft, it’s not hard to understand the feelings of Air Force test pilot Terry Pappas, who says that of all the planes he flew, the SR-71 “is at the pinnacle. When you walk up and look at it for the first time, it’s kind of hard to believe they built something like that.”

The speeds at which the Blackbird hurtled along resulted in extremely punishing conditions. Even though the SR-71 flew at altitudes higher than 96 percent of the atmosphere, there was still enough friction with air molecules to raise temperatures on the aircraft’s hull as high as 800 degrees Fahrenheit. Anticipating this, designers chose to build the SR-71 almost entirely out of titanium, a metal that is heat resistant and relatively lightweight but difficult to work with. In the early 1960s, it was also hard to find. One of the best sources was the Soviet Union, so the CIA, which also oversaw development of Blackbird’s predecessor, the A-12 Oxcart, set up shell companies abroad to purchase the metal from the very nation it was spying on.

To minimize its chances of being detected in enemy airspace, the SR-71 incorporated one of the first uses of stealth technology, including radar-absorbing composites for the leading edges and tail fins, and black paint impregnated with ferrite particles that soaked up radar energy. The aircraft’s distinctive shape, featuring blended fuselage and wings, and sharp-edged projections along the sides, was also chosen to minimize radar reflection.

Although flight testing began at the end of 1964, the first operational flight didn’t take place until 1968, during the Vietnam War. For the next two decades, the SR-71 would be called upon to photograph sites around the world that were beyond reach of spy satellites. Operating the battery of high-resolution cameras was the job of the reconnaissance systems officer in the back seat, while in the front seat, the pilot had his hands full just flying the airplane.

According to Pappas, one of 86 rigorously selected pilots who flew the Blackbird on missions, a dauntingly demanding aspect of the job was keeping the nose within one or two degrees of the prescribed angle—the only conditions under which the SR-71 was stable. At Mach 3, “you are hanging on to this vehicle which is on the edge of being out of control,” says Pappas. “That’s why your adrenaline is pumping the entire time you’re flying the airplane. That’s why you’re so tired at the end of a 31⁄2- hour flight.” Longer sorties, some lasting more than ten hours, were even more grueling.

And that was even if everything went perfectly; emergencies pushed the crew to its limit. The most unpleasant contingency, called an unstart, could erupt during a steeply banked turn, when airflow within an engine’s finely tuned inlet was disrupted, resulting in a sudden, drastic loss of thrust. Unstarts could be violent enough to slam a pilot’s helmet against the cockpit walls, even as he struggled to control the aircraft.

SR-71 pilots used to say, only half-joking, that unstarts were the Blackbird’s way of punishing them for letting their attention wander to the magnificent view from 80,000 feet. (One of the most memorable sights, available only to Blackbird pilots, was the sun rising in the west, as the aircraft overtook the earth’s rotation.) Nevertheless, says Pappas, “If I could sneak a look, I would. It was beautiful up there.”