During the Cold War the Soviet Union developed the Mikoyan-Gurevich MiG-25, a supersonic interceptor, and reconnaissance aircraft. Designed to intercept fast American aircraft like the SR-71 Blackbird, the MiG-25 Foxbat could reach Mach 3.2 – but unlike the aircraft it was designed to pursue, it carried four air-to-air missiles. It has remained one of the fastest military combat aircraft ever to fly.
However, the Soviet Union wasn't the only one to consider the possibility of an ultra-fast interceptor. For example, Lockheed developed the YF-12 as a potential replacement for the F-106 Delta Dart.
Development of the YF-12 was headed by Clarence "Kelly" Johnson, Lockheed's vice president for Advanced Development Projects – better known as the Skunk Works – in Burbank, California. Johnson had previously led the development of the U-2 spy plane and was charged to build an aircraft that could fly higher and even faster.
The project didn't begin entirely from scratch, however. In actuality, the YF-12 was the twin-seat version of the top-secret single-seat Lockheed A-12, and its design became the forerunner of the highly sophisticated SR-71 Blackbird strategic reconnaissance aircraft. Unlike the unarmed Blackbird, which used speed in its defense, the YF-12 was armed with three air-to-air missiles.
Only three of the YF-12 prototypes were ever built, and the first of those flew in August 1963, while two years later the first and third prototypes were used to set several records including a speed record of 2,070.101 mph and an altitude record of 80,257.65 feet. Pilot Col. Robert L. "Fox" Stephens and fire control officer Lt. Daniel Andrew received the 1965 Thompson Trophy for their speed record.
While both the records were surpassed by the Blackbird, the YF-12 has maintained its records for the largest, heaviest, and fasted manned interceptor to take to the skies. The prototypes were powered by two Pratt & Whitney J58 engines, which each provided 32,000 pounds of thrust with an afterburner, and it could reach speeds of Mach 3+. The aircraft had a ceiling above 80,000 feet and a range of 2,000 miles. As noted, it could carry three Hughes AIM-47A missiles. There were also considerations on how the aircraft could be used to deploy nuclear warheads.
The firing system was also notable in that it was controlled by two computers – considered quite sophisticated and powerful for their day. One was a digital computer for navigation and firing, while the other was an analog computer used for steering. In a test fire exercise a target drone was nearly shot down from 36 miles away at an altitude of 40,000 feet.
The program performed well enough, but it ended in 1968 – largely a victim of the ongoing war in Vietnam, as well as a lower priority on air defenses for the United States.
Two of the prototypes were recalled from storage in 1969 for a joint U.S. Air Force/NASA study of supersonic cruise technology. The aircraft was used in various NASA studies, which included in-flight heating, skin-friction cooling, "coldwall" research (a heat transfer experiment), flowfield studies, shaker vane research, and tests in support of the Space Shuttle landing program. The program ended in 1979.
Of the three prototypes, the first one was damaged beyond repair after a landing mishap while the third one was destroyed after the crew ejected to escape an in-flight. The second prototype built remains the only YF-12 in existence. It was flown to the National Museum of the United States Air Force in November 1979 and is currently on display in the Research & Development Gallery.
Peter Suciu is a Michigan-based writer who has contributed to more than four dozen magazines, newspapers and websites. He regularly writes about military small arms, and is the author of several books on military headgear including A Gallery of Military Headdress, which is available on Amazon.com.