The single PB-1 (P for patrol) was built in 1925 to a Navy requirement for a long-range, twin-engine flying boat capable of flying 2,400 miles nonstop from San Francisco to Hawaii. Construction material was primarily metal, but the top of the hull was made of wood and fabric covered the wings and tail. A Navy-built PN-9 made the nonstop flight to Hawaii in September 1925, so the PB-1 was never used for that purpose. Its designation was changed to PB-2 when the Navy removed the tandem Packard engines and installed experimental Pratt & Whitney Hornet air-cooled radials. The PB-1 incorporated many technical advances that would affect later Boeing designs, including the partly metal fuselage, wing spars of welded tube, and an improved Clark airfoil. Aerodynamically, it was a remarkably clean design for a flying boat.