——————Introduction——————
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).

——————Design&Armament——————

The main wing was swept at 55 degrees, and could be rotated around the spar to provide variable incidence. For takeoff and landing, the wing was tilted upwards to increase the angle of attack while keeping the fuselage nearly horizontal.

The larger vertical fin was supplemented by a ventral fin for high-speed stability. This fin can be folded during takeoff and landing to avoid hitting the ground.

The cockpit design originally featured a canopy, but low drag requirements for high speed suggested that it be removed.The system shown on mockups used two large oval windows on the cockpit sides, and a periscope system projecting an image onto a fresnel lens arrangement directly in front of the pilot.

Weapons were carried in bays located on the sides of the fuselage behind the cockpit, which opened by flipping upward, thereby rotating the missiles out of their bays. It was to be armed with a likely arrangement of three or four each GAR-1s and GAR-3s, fired in pairs (one each radar and infrared guided) to improve the odds of a hit. The XF-103 also was to feature 36 2.75-inch "Mighty Mouse" FFARs.

——————Features&Controls——————
-Internal missile bays (hold 'fire weapons' key to activate)
-Adjustable main wings (AG7+VTOL)
-Auto-deployed tail fin (Landing gears)
-Custom landing gear
-Normal flight controls
-Rotatable wingtips

*it's struggling to keep level flight,but I don't know how to solve it…and difficult to land.