Curtiss / Naval Aircraft Factory F-5-L Flying Boat

The F-5-L was a large twin-engine patrol flying boat, the standard long-range maritime patrol aircraft of the U.S. Navy in the years after World War I. It was an Americanized development of the British Felixstowe F.5, re-engined with two 400 hp Liberty 12A engines in place of the original Rolls-Royce Eagles. The existing label is doubly inaccurate: it should read 'F-5-L' rather than 'F-51,' and the type was not built by Martin.

Production was shared among the Naval Aircraft Factory, which flew the prototype in July 1918 and built the majority, along with Curtiss and Canadian Aeroplanes Ltd. Crewed by four, the biplane boat carried six to eight flexible .30 in machine guns and could lift several hundred-pound bombs for anti-submarine and patrol work. F-5-Ls remained the Navy's primary flying boats until the late 1920s, when the PN series superseded them.