During the most intense period of the Cold War, the battle for control of the skies was merciless. The United States and the Soviet Union were competing in a technological arms race, where they would test each other’s limits repeatedly in terms of speed, altitude, and weaponry. Speculation about the Soviets having supersonic spy planes and bombers fueled the imaginations of American defense planners, who were eager to outdo one another.
They didn’t dream of an interceptor that would catch the bad guys; they dreamed of one that would leave them in the dust. The outcome of that vision was the Lockheed YF-12, a plane that temporarily held the title for being the fastest and highest-flying interceptor in the world, a testament to the audacious vision of American aerospace engineering.
The YF-12 was essentially an offshoot of the A-12, a clandestine spy plane that Lockheed’s Skunk Works division constructed in secrecy under the leadership of Clarence “Kelly” Johnson. The A-12 was constructed to replace the U-2 spy plane, and when it took to the skies for the first time in 1962, the world was introduced to the steady speed of over Mach 3, a new standard for all time, which dramatically changed what people believed could be accomplished with aircraft.
But the Air Force was not satisfied with just a spy plane. They required a new-generation interceptor to replace the F-106 Delta Dart to protect North American skies against possible Soviet bomber attacks. When the XF-108 Rapier program was canceled, Lockheed suggested converting the A-12 into a two-seat interceptor. With improved radar, heavy missiles, and a second cockpit for a weapons systems officer, the idea developed into the YF-12.
This makeover was no small thing. The nose of the plane needed to be redesigned to accommodate the massive Hughes AN/ASG-18 pulse-Doppler radar, originally destined for the XF-108. Weighing more than 2,100 pounds and lumbering along, it could detect targets 100 miles off. Two infrared search-and-track sensors allowed the plane to detect and follow aircraft flying beneath it. Its four camera bays were re-purposed to carry three AIM-47 Falcon missiles with Mach 4 speeds and a 100-mile range. Its aerodynamic enhancements, ventral fins, gave the YF-12 its sleek, pointed appearance.
Beneath its sleek aerodynamic curves, the YF-12 was a marvel of engineering. Its titanium body could sustain the blistering heat of speeds above Mach 3. Two Pratt & Whitney J58 engines, generating more than 32,000 pounds of thrust each, propelled the plane on special JP-7 fuel. Wingtips at top speed would be blinding white, and the plane could climb higher than 80,000 feet, well beyond the reach of most air defenses in the first decades.
Performance of the YF-12 was fabulous. On May 1, 1965, it established official world records, flying 2,070 mph and to a height of 80,257 feet. In one dazzling test, a missile, fired from 74,000 feet at Mach 3.2, hit a B-47 drone 500 feet high—a clear indication of what it could do.
Though its performance was unparalleled, the YF-12 was never produced in mass quantities. The Air Force originally intended to purchase 93 F-12B interceptors, but changing priorities, increasing costs, and the Vietnam War caused Secretary of Defense Robert McNamara to order appropriations cancellations. Additionally, with the Soviets emphasizing ballistic missiles rather than bombers, the demand for a Mach 3 interceptor diminished. The program was canceled in 1967 after the production of only three YF-12As, mostly for testing.
But the YF-12 had a lasting impact. The technologies it incorporated directly were input to the SR-71 Blackbird, a plane that would be the stuff of legend as a spyplane. Radar and missiles developed on the YF-12 also influenced the AWG-9 radar and AIM-54 Phoenix missile employed by the F-14 Tomcat.
Even with the program’s cancellation, the YF-12s were employed by NASA and the USAF as test aircraft, and they gained invaluable experience in the development of supersonic and hypersonic flight, which would go on to shape projects that ultimately involved the Space Shuttle.
Now, only one of the original YF-12As remains, preserved at the Dayton, Ohio, United States Air Force National Museum. It is a testament to an era of experimentation during which engineers pushed the envelope of speed, altitude, and technology. Although never engaged in combat, the innovations of the YF-12 continue to echo in the high-speed planes that followed.