For a brief shining moment, the U.S. Air Force was poised to fly the fastest, arguably the most badass. fighter jet of all time. The jet, the YF-12A, was one of several variants offered in the SR-71 Blackbird family of high-speed jet aircraft in the 1960s. Yet an operational version of the aircraft has not was never put into production, as world events and developments in the United States nuclear politics made it a questionable choice. Today, the YF-12A remains the closest the United States has ever come to producing an armed aircraft capable of Mach 3.

On May 1, 1960, the Soviet Union shot down a U-2 spy plane over the USSR with its S-75 “Dvina” surface-to-air aircraft. missile . Central Intelligence Agency pilot Francis Gary Powers flew the high-flying but slow-flying U-2 and took photos of the Soviet Union. The CIA had hoped that the photos would help formulate estimates of Soviet military power, but the capture of Powers and the loss of his aircraft meant that the U-2 was no longer invulnerable to Soviet air defenses. A new aircraft was needed to continue the flyover program.

One was already in preparation. In 1959, Lockheed’s Advanced Development Programs Division, or its current nickname, “Skunk Works”, presented plans to the CIA for a Mach 3 reconnaissance aircraft named the Oxcart. Later called the A-12, it was designed to perform the same mission as the U-2, with belly-mounted cameras capable of photographing large areas of the ground below. But the A-12 would fly faster and be much harder to detect than its predecessor.

THE A-12 HAD A PIONEERING AIRCRAFT DESIGN. The aircraft was 101 feet long, much longer than most tactical aircraft of the time, and used two new J58 turbojet engines integrated into the wings, an unusual design: the engines were usually located in the fuselage. The two engines, producing a total of 65,000 pounds of thrust in afterburner mode, would allow the aircraft to fly at Mach 3.1, giving air defense systems like the S-75 very little time to react. This was unprecedented at a time when the fastest fighter at the time, the F-106 Delta Dart, could only support Mach 2.6. The wide, blended design of its wings and body gave it plenty of internal volume for fuel, allowing it to achieve a range of 2,900 miles before needing to refuel. The plane would fly up to 95,000 feet, about three and a half times the height of Mount Everest, allowing cameras to photograph a vast panoramic view of the countryside below.

The A-12 was the first aircraft designed with stealth in mind. President Dwight D. Eisenhower, who had taken a particular interest in the program, wanted the plane to be invisible to radar, to avoid any embarrassing incident in which a plane would be lost while intruding into enemy territory. A CIA study concluded that it is possible to reduce an aircraft’s radar signature. So Lockheed got to work modifying the A-12 design, blending the wings and fuselage as much as possible to reduce the number of vertical surfaces. The design also swapped its large vertical rear wing, known as the vertical stabilizer, for two smaller angled stabilizers. The angled stabilizers presented a smaller surface area to incoming radar waves, reflecting less energy onto enemy radars and making the aircraft more difficult to detect.

As the A-12 entered production, Lockheed quietly approached the Air Force about a weaponized variant of the new jet; until then, the Air Force had been excluded from efforts to build an unarmed spy plane. The Air Force enthusiastically agreed, and three A-12s in production were diverted to a new and mysterious program known only as KEDLOCK. The plane would have an important mission in the nuclear age: to eliminate enemy bombers.

THE THREAT OF ATOMIC BOMB ATTACK HAS BECOME REALITY once, long-range B-29 bombers dropped an atomic bomb on the Japanese cities of Hiroshima on August 6, 1945, and Nagasaki three days later. When the Soviet Union became the second country to develop nuclear weapons in 1949, nuclear threat extended against the United States The Soviet R-7, the world’s first intercontinental ballistic missile, still poses no real threat, with a range of only 5,000 miles. Until the early 1960s, the heavy bomber was still the primary means of delivering an atomic bomb to a target, and the United States continued to develop a defensive fighter capable of intercepting and shooting down any bomber .

In 1953, the Air Force began developing a new interceptor intended to protect the United States and Canada from attacks by Soviet bombers. North American Aviation’s XF-108 Rapier was a large fighter designed to fly at Mach 3 and an altitude of 60,000 feet. From its commanding position in the sky, the Rapier would encounter Soviet bombers as they attempted to penetrate American airspace via the North Pole. A new, highly advanced radar, the AN/ASG-18, would allow the XF-108 to detect bombers 100 miles away and flying as low as 500 feet. The Rapier was supposed to be armed with three GAR-9A air-to-air missiles, each with a maximum speed of Mach 4. Each missile would be equipped with a 0.25 kiloton nuclear warhead, ensuring the destruction of the bombers. However, this ambitious program became too expensive and the change in US nuclear strategy made the plane less necessary. In 1959, the Pentagon canceled production of the XF-108 Rapier.

Despite this setback, the prospect of a Mach 3 fighter had whetted the Air Force’s appetite for top speed. And despite the loss of the Rapier aircraft, its radar and key weapons system, the AN/ASG-18 and GAR-9 missiles, showed promise. The stage was set for a new aircraft that would carry the torch. In the deserts of Nevada, Lockheed had the answer to the continuing need for a new high-speed interceptor.

The Lockheed A-12 is a retired high-altitude reconnaissance aircraft that could fly at Mach 3 and beyond. Lockheed’s Skunk Works built it for the CIA, and it was the precursor to the US Air Force’s YF-12 interceptor prototype.

THE KEDLOCK PROGRAM WAS A COVERED EFFORT TO BUILD AN ARMED A-12. Lockheed workers kept three planes in the A-12 production shop, but separately from other projects, in order to modify them in secret. To confuse Soviet spies, they bore the designation A-11, that of a previous unsuccessful spy plane.

The YF-12s that the United States kept secret were very similar to the A-12 externally, except for a rounded conical fairing, like that of the F-14 Tomcat fighter. This fairing concealed the nose-mounted 40-inch AN/ASG-18 radar, which did not fit into the existing A-12 nose design. This ended up giving the YF-12 a radically different shape, similar to that of a fighter jet.

The YF-12 traded the A-12’s Perkins Type I stereographic camera system for three GAR-9 missiles. They were stored in three payload bays below and behind the cockpit. The YF-12 conducted its first unpowered drop test with a GAR-9 in April 1964, but the test failed: the missile separated, pitching up. If a rocket engine had ignited, it would have slammed straight into the plane’s cockpit. However, less than a year later, a YF-12 achieved its first aerial kill, downing a target 36.2 miles away. During a test in September 1965, a YF-12 launched another GAR-9, from an altitude of 75,000 feet at a speed of Mach 3.26, scoring another interception at a similar distance.

The YF-12 was always intended to be a technology demonstrator. Now that the technology had proven itself, engineers put the production aircraft version, the fighter-bomber combination, designated FB-12, on the drawing board. Even more ambitious than the YF-12, the FB-12 was intended to carry both the GAR-9 missile (later known as the AIM-47 Falcon) and the short-range attack missile, or SRAM. The SRAM was an air-to-ground nuclear strike missile with a range of approximately 130 miles and a 17-kiloton warhead, greater than the 15-kiloton power of Hiroshima’s “Little Boy” bomb. SRAM would likely allow the FB-12 to fly deep into Russia, attacking ground targets in concert with larger nuclear bombers.

The Air Force secured funding for 93 FB-12 fighters, but the planes were never built. Once again, a change in nuclear strategy left aircraft without a useful role. American military policy no longer required shooting down enemy bombers, but shifted toward a strategy that deterred the enemy from launching an attack. Meanwhile, a fighter-bomber armed with short-range nuclear missiles competed for the Air Force budget with the XB-70 Valkyrie bomber, capable of Mach 3. The FB-12 was fast, but he couldn’t outrun a changing world. Although it came close, the U.S. government never built a Mach 3 interceptor.

Over time, combat aircraft design placed less emphasis on speed in favor of maneuverability, weapons capability, aircraft range, and stealth. But you can still see one of the three remaining YF-12As on display at the National Museum of the US Air Force in Dayton, Ohio. NASA has leased the other two for research purposes.

The A-12 range left behind a proud lineage of work in 32 SR-71 Blackbirds. Thanks to their muscular capabilities, the Blackbird can be considered a direct descendant of the A-12. The Air Force still got its Mach 3 planes, at least until they were removed from service in 1999.