The Curtiss XP-31 Swift (Wright Field Project Number XP-934) was a 1930s American experimental monoplane fighter built by Curtiss for the United States Army Air Corps.

The XP-31 featured the first enclosed cockpit on a U.S. pursuit aircraft and was also the last pursuit aircraft to have fixed landing gear and externally braced wings.

Curtiss offered the XP-31 (given the Wright Field Project Number XP-934) in a 1932 competition with the P-26. It was a low-wing monoplane with fixed landing gear, first flown in July. It was the AAC's first single-seat closed-cockpit fighter, and the last with fixed gear and wing struts. Despite its small size, it was badly overweight, and carried 125 gallons (104 imp gal, 474 L) of fuel. Although Curtiss considered the design significant in that it introduced various new technologies, compared to its contemporaries the XP-31 was already outmoded, and, more importantly, testing showed that it fell below performance expectations.

Despite its innovations, the XP-31 did not offer any advantages compared to its rival the Boeing P-26 Peashooter and was not ordered into series production.

​