North American XF-108 Rapier

The North American XF-108 Rapier was a proposed long-range, high-speed interceptor aircraft designed by North American Aviation intended to defend the United States from supersonic Soviet strategic bombers. The aircraft would have cruised at speeds around Mach 3 (3,200 km/h; 2,000 mph) with an unrefueled combat radius over 1,000 nautical miles (1,900 km; 1,200 mi), and was equipped with radar and missiles offering engagement ranges up to 100 miles (160 km) against bomber-sized targets.

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 program had progressed only as far as the construction of a single wooden mockup when it was canceled in 1959, due to a shortage of funds and the Soviets' adoption of ballistic missiles as their primary means of nuclear attack. Had it flown, the F-108 would have been the heaviest fighter of its era.

Prior to the project's cancellation, U.S. President Dwight D. Eisenhower noted that raising the F-108 interceptor force would have cost the U.S. taxpayer $4 billion (equivalent to $43 billion today).