A
flying boat is a
fixed-winged seaplane with a
hull, allowing it to land on water, that usually has no type of landing gear to allow operation on land. It differs from a
floatplane as it uses a purpose-designed
fuselage which can float, granting the aircraft
buoyancy. Flying boats may be stabilized by under-wing
floats or by wing-like projections (called
sponsons) from the fuselage. Flying boats were some of the largest aircraft of the first half of the 20th century, exceeded in size only by
bombers developed during World War II. Their advantage lay in using water instead of expensive land-based runways, making them the basis for international
airlines in the
interwar period. They were also commonly used for maritime patrol and
air-sea rescue.