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The Rise and Fall of the XF-108 Rapier: A Supersonic Dream Deferred

Now, in the late 1950s, a scenario was playing out for the United States no less chilling than this: one where the DEW Line detected dozens of Soviet bombers flying across the North Polar region, each armed with thermonuclear warheads that could wipe out American cities. Something was desperately needed to counter the menace, and it had better be fast. The Air Defense Command of the U.S. Air Force required an interceptor able to effectively neutralize the threat. The XF-108 Rapier was a project that seemed to be the most technologically ambitious fighter interceptor of its time.

By 1955, the Soviet Union had unveiled its latest bombers: the jet-powered Tupolev Tu-16 Badger and Myasishchev M-4 Bisons, and turbo-prop-powered Tu-20 Bears. Intelligence revealed that a supersonic delta-wing bomber was being developed. The U.S. Air Force, still lacking an operational supersonic aircraft, then issued a general operating requirement in October 1955 for a new interceptor capable of sustained velocities of Mach 3, an operational ceiling above 75,000 feet, and the range to loiter around interception points for an hour.

As a result of this, North American Aviation became the prime contractor for this project, which received the designation XF-108A. The design work was based on North America’s earlier unmanned X-10 test vehicle and shared many components with the XB-70A Mach 3 bomber. The XF-108A was planned not only as an interceptor at high speed but also as escort ammunition for the B-70 bomber, sharing in structure and most systems.

The XF-108A later christened the Rapier, was conceived as an unusually powerful aircraft. It was to be powered by two General Electric J93-GE3-AR engines, rated at 30,000 pounds of thrust in full afterburner. One AIM-47 missile flew at Mach 6 and had a range beyond 100 miles. Hughes Aircraft had developed a cutting-edge AN/ASG-18 radar and fire-control system for the XF-108A, allowing it to lock onto targets and launch missiles from standoff distances.

Even with this amazing potential, the XF-108A project was in trouble. In 1959, ICBM development suddenly shifted the priorities of defense. The proponents said that ICBMs were cheaper, quicker, and more accurate than high-altitude Mach 3 bombers and interceptors. As a consequence, the XF-108A was canceled in September 1959. A total of $141.9 million had been invested in research and development. The XB-70A bomber program was cut back to a single experimental prototype.

Although the Rapier itself never left the drawing board, its technology did. The A3J {A-5/RA-5) Vigilante Navy attack and reconnaissance aircraft, built by North Americans, carried over many features of the XF-108. Hughes’s ASG-18 fire-control system and AIM-47A missiles found another use in Lockheed YF-12A, a single-seat version of the SR-71 Blackbird. The Soviet Union was influenced by both the XF-108 and XB-70 projects when it developed the Mikoyan-Gurevich MiG-25 Foxbat.

The XF-108 Rapier may have never taken off, but it remains the monument to the bold, creative spirit that forged Cold War military aviation.

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