A fixed-wing aircraft that lands on and takes off from water. There are two types. The floatplane (known as a seaplane in the UK) has a conventional fuselage with floats, shaped like a boat’s hull, attached below the fuselage, replacing the undercarriage. The aircraft rests on the floats while on the water with the fuselage held clear of the surface. The fuselage of a flying boat resembles a boat and sits in the water, usually with floats beneath the wings to stabilize it. Amphibious aircraft are seaplanes that also have a conventional undercarriage with wheels that lower to below the level of the floats, so that they are able to operate from terrestrial airfields. Seaplanes have the advantage of not requiring landing fields, being able to operate anywhere with an expanse of calm water. Floatplanes are unable to operate in waves higher than about 30 cm; flying boats can operate in larger waves and some require waves during take-off to allow the aircraft to rock on to a step in the hull. Flying boats are larger than floatplanes and carry larger payloads. Seaplanes were used extensively during the first part of the twentieth century, but their use declined after World War II because of the large increase in the number of airfields. Floatplanes are still used in some remote locations.