XP-55 Ascender (CW-24), was a 1940s United States prototype fighter aircraft built by Curtiss. Along with the XP-54 and XP-56, it resulted from USAAC proposal R-40C issued on 27 November 1939 calling for unconventional aircraft designs. A highly unusual design for its time, it had a canard configuration, a rear mounted engine, swept wings and two vertical tails. Like the XP-54, the Ascender was initially designed for the Pratt & Whitney X-1800 engine and had to be redesigned when that engine project was cancelled. It would also be the first Curtiss fighter aircraft to use tricycle landing gear.