Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The North American XF-108 Rapier was a proposed American design for a long-range, high-speed interceptor aircraft to defend the United States and Canada from supersonic Soviet bombers. A very high performance, long-range interceptor had been proposed by the USAF as early as 1952, but formal development of what became known as the Long-Range Interceptor, Experimental (LRI-X) was not approved until 20 July 1955. The specification was laid down on 6 October, calling for an interceptor that could fly at 60,000 ft (18,000 m) at a speed of Mach 1.7 (1,122 mph (1,806 km/h) at that altitude) with a range of 1,150 miles (1,850 km). It was to have a two-man crew, at least two engines and a powerful radar.