Republic XF-103

XF-103
Artist's impression of the XF-103
Role	Interceptor
Manufacturer	Republic Aviation
Designer	Alexander Kartveli and William O'Donnell
Status	Canceled at mock-up stage
Program cost	US$104 million for the program

The Republic XF-103 was an American project to develop a powerful missile armed interceptor aircraft capable of destroying Soviet bombers while flying at speeds as high as Mach 3 (2,300 mph; 3,700 km/h). Despite a prolonged development, it never progressed past the mockup stage.

In 1949, the USAF issued a request for an advanced supersonic interceptor to equip the Air Defense Command. Known formally as Weapon System WS-201A, but better known informally as the 1954 interceptor, it called for a supersonic aircraft with all-weather capability, intercept radar and air-to-air missile armament. Republic was one of six companies to submit proposals. On 2 July 1951, three of the designs were selected for further development, Convair's scaled-up XF-92 that evolved into the F-102, a Lockheed design that led to the F-104, and Republic's AP-57. AP-57 was an advanced concept to be built almost entirely of titanium and capable of Mach 3 at altitudes of at least 60,000 feet (18 km).

A full-scale mock-up of the AP-57 was built and inspected in March 1953. A contract for three prototypes followed in June 1954. Work on the prototypes was delayed by continued problems with the titanium construction, and more by continuing problems with the proposed Wright J67 engine. The contract was later reduced to a single prototype. In the end, the J67 never entered production and the aircraft it had been chosen for were forced to turn to other engine designs, or were cancelled outright. Republic suggested replacing the J67 with the Wright J65, a much less powerful engine. The project was eventually cancelled on 21 August 1957 with no flying prototypes ever being completed.

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