In June 1938, the U.S. Navy signed a contract with Vought for a prototype bearing the factory designation V-166B, the XF4U-1, BuNo 1443. The Corsair design team was led by Rex Beisel. After mock-up inspection in February 1939, construction of the XF4U-1 powered by an XR-2800-4 prototype of the Pratt & Whitney R-2800 Double Wasp twin-row, 18-cylinder radial engine, rated at went ahead quickly, as the very first airframe ever designed from the start to have a Double Wasp engine fitted for flight. When the prototype was completed it had the biggest and most powerful engine, largest propeller, and probably the largest wing on any naval fighter to date. The first flight of the XF4U-1 was made on 29 May 1940, with Lyman A. Bullard, Jr. at the controls. The maiden flight proceeded normally until a hurried landing was made when the elevator trim tabs failed because of flutter.