The XP-54 was a prototype fighter built by the Vultee Aircraft Company. They had submitted a proposal in response to a USAAC request for an unusual configuration. The Vultee design won the competition, beating the Curtiss XP-55 and the Northrop XP-56 Black Bullet. Vultee had designated it Model 84, a descendent of their earlier Model 78. After completing preliminary engineering and wind tunnel tests, a contract for a prototype was awarded on January 8, 1941. A second prototype was ordered on March 17, 1942. Flight tests of the first prototype began on January 15, 1943. Initial trials showed performance substantially below guarantees. At the same time, development of the XH-2470 engine was discontinued and, although it appeared possible to substitute the Allison 3420 engine without substantial airframe changes, the projected delay and costs resulted in a decision not to consider production buys. The prototypes continued to be used in an experimental program until problems with the Lycoming engines and lack of spare parts caused termination.