The aerospace firm North American Aviation designed the XF-108 as a long-range interceptor. Its primary mission would have been to intercept Soviet strategic bombers that were en route to the United States—with American cities in their crosshairs. To fulfill this hypothetical mission, the U.S. Air Force issued several stringent design requirements.

They XF-108 would have to fly fast and high—about 60,000 feet, at a minimum speed of Mach 1.7—all while having at least a 1,000 mile range. As an interceptor, the XF-108 would have to be able to target and shoot down Soviet nuclear bombers and was therefore to be equipped with a powerful new radar. Though it was not implemented on the XF-108, this radar would have made the interceptor the first jet with a look down/shoot down capability. It would also would have been able to detect and lock onto targets below the horizon—making it the first airplane able to accurately hit targets beyond the horizon.

The radical new radar was to be paired with an equally radical air-to-air missile, the AIM-47. Originally designated the GAR-9, the missile could be equipped with conventional explosives—or a small nuclear warhead. Despite the XF-108 project cancelation, the missile’s capabilities would continue to grow, eventually achieving a range of over 100 miles per hour. 

Though the XF-108 design varied somewhat throughout its short lifetime, the final design used a type of modified delta wing design. This large wing design offered some aerodynamic advantages over conventional wing designs during high subsonic, transsonic, and supersonic flight. It also allowed a much greater volume of fuel to be stored internally inside the wing, significantly increasing the XF-108’s potential range.

Thanks partly to the XF-108’s wide hypothetical range, North American Aviation proposed the XF-108 as a fighter complement to their XB-70 Valkyrie strategic nuclear bomber project. In this role, the XF-108 would have used its good range and phenomenal speed to keep Soviet interceptors at bay, away from America’s nuclear-armed bombers during a war.

Postscript

Ultimately the XF-108 never made it past a single wooden mockup. Though the jet was decidedly modern looking and would have been quite capable, the interceptor role it was designed for was no longer needed by the late 1950s. Both the United States and the Soviet Union shifted nuclear delivery from bombers to intercontinental ballistic missiles. There was therefore no longer a Soviet bomber threat, at least not of the importance that the Air Force had originally envisioned. So much for the XF-108 Rapier—it would have been a phenomenal interceptor. 

Caleb Larson is a Defense Writer with The National Interest. He holds a Master of Public Policy and covers U.S. and Russian security, European defense issues, and German politics and culture.

Image: Reuters