In September 1924, the Naval Aircraft Factory was tasked with designing a long-range twin-engined flying boat, capable of flying the 2,400 mi (3,860 km) between San Francisco and Hawaii. The initial design was carried out by Isaac Laddon, an employee of Consolidated Aircraft, and then passed to Boeing for detailed design and construction. The new flying boat, the Boeing Model 50, was a two-baybiplane of very streamlined design for flying boats of the time. The wings were of metal construction, with wooden wingtips and leading edges. The fuselage had a metal lower part, with the upper half made of laminated wooden frames with a wood veneer covering. Two 800 hp (600 kW) Packard 2A-2500V12 engines driving four-bladed propellers were mounted in tandem between the wings above the fuselage.
The Boeing Model 50, designated XPB-1 by the US Navy, made its maiden flight in August 1925. It was intended to use it to lead a pair of Naval Aircraft Factory PN-9s in an attempt to fly to Hawaii on 31 August 1925, but engine trouble led to its participation in the flight being cancelled. In 1928, the aircraft was modified by the Naval Aircraft Factory, its Packard engines were replaced by two 500 hp (370 kW) geared Pratt & Whitney R-1690 Hornet radial engines, leading to the new designation XPB-2.