The Model 31 was a new flying boat design started in 1938, intended for both military and commercial use.

The aircraft was of all-metal construction with a high-mounted, high-aspect ratio cantilever monoplane wing (the Davis wing, which was later used in the B-24 Liberator)[1] and an upswept aft fuselage with a tail unit with twin endplate fins and rudders.

[2] The Japanese attack on Pearl Harbor on 7 December 1941 brought America into the Second World War just as testing was complete and the United States Navy purchased the prototype, designated XP4Y-1, which was converted into a prototype patrol aircraft, fitted with nose, tail and dorsal gun turrets and 4,000 lb (1,820 kg) of external stores.

Delays in preparation of the prototype and the shortage of Wright Duplex Cyclone engines (which were required to power the B-29 Superfortress) led to the production order being cancelled, with the factory being used to build the PBY, instead.

[4] Data from The Illustrated Encyclopedia of Aircraft (Part Work 1982–1985), 1985, Orbis Publishing, p. 1194General characteristics Performance Armament