Republic F-103 side and frontal views, US Patent. Note the original conventional canopy arrangement.
Republic had begun work on a high-Mach interceptor in the late 1940s, and by the time that the USAF was looking for a "1954 Interceptor" plans had gelled around the AP-57 design. This beast of an aircraft, to be designated as the XF-103 by the USAF, was to have been nearly as long as a B-47 bomber, and intended to have a top speed verging on Mach 4. This performance was to have been achieved through the use of a dual cycle powerplant arrangement, fed through a large ventral intake scoop. The conventional turbojet portion, a Bristol Olympus built by Curtiss-Wright as the XJ67, would have powered the aircraft up to Mach 2; for high-speed dashes, a Wright XRJ55 ramjet would be phased in above that speed, taking the XF-103 to Mach 3.7 and 73,000 feet. Like the later SR-71, the XF-103 would have been built primarily of titanium to cope with the immsense heat loads; the Thunderwarrior was at first intended to have a conventional canopy, but this was later changed to a flush window arrangement (with periscope for landing) in order to better cope with the heat.
Armament was to have consisted of four AIM-4 Falcons fired from retractable launchers extended from the forward fuselage, plus three dozen Mighty Mouse rocket launchers.
The XF-103 mockup was completed by the spring of 1953, and three prototypes were contracted for. Progress was slow, post-Korea budgets put the program at risk, and by the time the plug was pulled in August 1957, the whole affair had been downgraded to a single aircraft that would have been used for research work.
Lloyd S. Jones U.S. Fighters Army-Air Force 1925 to 1980s p.275-277 includes a 3-view and photo of the XF-103 mockup.
Anigrand Craftsworks makes a 1/72 scale XF-103 kit in resin.