The armament consisted of six .50 caliber (12.7 mm) wing-mounted Browning AN/M2 machine guns and underwing racks for two 1,000 lb bombs; Alternative armament packages included two 37 mm M4 autocannons with four .50 caliber AN/M2s, or four M4 autocannons.

The XP-72 development paralleled that of another Republic design, the XP-69 that was to be powered by an experimental 42-cylinder Wright R-2160 liquid-cooled inline radial engine mounted in the nose of the aircraft and driving contra-rotating propellers.

[1] The XP-69 was intended for high altitude operations and featured a pressurized cockpit and armament of two 37 mm cannon and four 50 caliber machine guns.

As the XP-72 displayed exceptional performance during flight tests, an order for 100 production aircraft was awarded.

By this time, World War II had progressed to where the need was for long-range escort fighters and not high-speed interceptors.