The XF-108 Rapier program never progressed past the mock-up stage, a victim of changing technology.
During the Cold War, the threat posed by Soviet long-range strategic bombers prompted American strategic planners to come up with countermeasures. One of those ambitious projects was the North American XF-108 Rapier, a high-speed, long-range interceptor aircraft designed by North American Aviation intended to defend the United States from supersonic Soviet strategic bombers.
To limit development costs, the program shared engine development with the North American XB-70 Valkyrie strategic bomber program, and used a number of elements of earlier interceptor projects. The aircraft would have cruised at speeds around Mach 3 with an unrefueled combat radius over 1,000 nautical miles, and was equipped with radar and missiles offering engagement ranges up to 100 miles against bomber-sized targets. The aircraft was powered by two General Electric J93 turbojet engines, also used in North American’s XB-70 Valkyrie bomber, in the fuselage.
The initial F-108 configuration featured a very large “cranked” delta wing. There were fixed ventral stabilizers on the wings, mounted at mid-span, and a tall all-moving vertical tailfin, supplemented by two ventral stabilizers that extended when the landing gear retracted. Although some earlier versions of the design had separate tailplanes or forward canards, both were abandoned in the final design.
The F-108 was intended to carry the Hughes AN/ASG-18 radar, the U.S.’s first pulse-Doppler radar set. The radar was used to guide the Hughes GAR-9 air-to-air missile, three of which would be carried on a rotary launcher in an internal weapons bay. The GAR-9 was a very large, long-range weapon with its own radar set for terminal homing. It was intended to fly at Mach 6, with a range of almost 112 miles.
Ultimately the XF-108 Rapier program never progressed past the mock-up stage, a victim of changing technology. In the 1950s and 1960s, both the Soviet Union’s and the United States’ nuclear weapon delivery transitioned almost completely from long-range strategic bombers to intercontinental ballistic missiles, making interceptors significantly less important for homeland defense.
Still, the Rapier design effort was not entirely in vain: the North American A-5 Vigilante retained some parts of the Rapier design, including fuselage and parts of its weapon system and was in some ways a smaller, less-ambitious Rapier-like design.