Early 1939, USAAC recognized need to develop advanced pursuit aircraft to counter potential threat of German and Japanese counterparts. Until then, most new designs privately funded; only P-38, P-39 and P-40 under development . Engine development also lagging. In effort to develop one or more advanced types to be mass-produced in FYs 1941-2, FY 1941 Air Corps R&D Program for experimental aircraft authorized; $2.4 M available for basic development and $3.6 M for prototypes of promising designs. Approval for XP- 46--a higher-performance P-40--and Republic XP-47 followed, but Air Corps still felt more advanced designs were possible. Accordingly, Request for Data R-40C released. 3 pusher designs selected-- Vultee XP-54, Curtiss XP-55, and Northrop XP-56, a tailless interceptor using Northrop flying wing technology tested earlier. Had short fuselage mounted on swept-back wing with dorsal and ventral fins. Engine was cooled by air from wing-root intakes passing through wings. Utilized welded magnesium construction, had tricycle gear, drooped wing tips, air-operated bellows-type rudders, and elevon control surfaces. Armament included 2 20 mm guns and 4 50 cal guns. Estimated top speed about 465 mph at 19,500 ft, but it only reached 250 mph on one occasion. 2 prototypes ordered. Plagued with 2 problems: engine hurried into development and had serious flaws. Northrop apparently extrapolated N-1M Flying Wing design to XP-56 and had some miserable control problems. Combination of engine and control problems too much. On third flight, first prototype crashed spectacularly as it was about to break ground; left tire blew and aircraft swung sharply to left eventually somersaulting backwards 2 times before coming to rest upside down. Pilot John Myers thrown clear and miraculously escaped with only minor injuries mainly becaue he was wearing an old polo helmet which protected his head. Second prototype had better tires and modified rudder control system but did not fare much better. After 10 flights and serious recurring difficulties, program ended May 44. P- 47 had by then been in production for 18 months and had much better performance than XP-56; XP-55 was equally disappointing. Soon after, promise of jet-powered aircraft ended all interest in piston-engine fighters.