Float planes, or seaplanes, relied on pontoons, rather than on displacement hulls like the flying boats, for buoyancy on the water. In US usage, they were used primarily as scout-observation planes flying from capital ships — cruisers and battleships. They also found some use as small transports flying into undeveloped areas, where they could land on and take off from available water, not requiring an airstrip or aerodrome to be built. A few were used for patrols, mostly coastal patrols, where they could operate out of estuaries or near-shore lakes or rivers. Float planes were often offered in an alternate wheeled configuration for operating from fixed land bases.

It was found that a single pontoon, with outriggers near the wingtips that were primarily for stability rather than for flotation, handled better in rough water than dual pontoons. Larger planes, however, and those that could count on operating from fairly smooth water, tended toward the dual pontoons, which offered more buoyancy. German and Italian float planes were mostly dual-pontoon designs.

The primary American float planes were the Vought OS2U Kingfisher and the Curtiss SO3C Seagull. Both were used from capital ships and from land bases. The Curtiss SC-1 Seahawk appeared late in the war.

German Arado Ar-196, Blohm & Voss Ha-139 and Ha-140, Dornier Do-22, Focke-Wulf Fw-62, Heinkel He-59, He-114, He-115 and He-119, and the Italian Cant Z-506B torpedo plane were all dual-pontoon designs. Even some Ju-52s were fitted with dual pontoons and used in the invasion of Crete.

Japan's Aichi Jake and Yokosuka Glen were twin-float designs, while the Kawanishi Rex and the Mitsubishi Rufe and Rex were single-float designs.

Britain's Fairey Seafox and Fokker T.VIII were both twin-float designs. Sweden also had a dual-pontoon reconnaissance plane.

In addition to planes designed as float planes, a variety of other planes were experimentally fitted with floats.

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