The XF-103 was developed as a high-speed high-altitude aircraft specifically designed to intercept incoming enemy bombers. The XF-103 was proposed in the same contract competition that resulted in the Convair F-102--Project MX-1554 Interceptor Fighter Airplane. The Republic design, Model AP-57, underwent a design performance evaluation conducted by the Air Material Command (AMC). The results showed an estimated top speed of 1438 knots. A limiting Mach number of 3.0 was quoted due to excessive (estimated) turbine inlet air temperature. The Republic AP-57 design was ranked 8th out of 9 entries for design. The only aircraft scoring lower (as a design) was the Consolidated-Vultee (i.e. initial F-102 design) entry.
The USAF canceled the XF-103 development contract on 21 August, 1957 when the aircraft was in the mock-up phase.