Pontoon bridge is a bridge supported by pontoons (flat-bottomed boats), metal cylinders, or other portable floats. A pontoon bridge is sometimes called a ponton bridge. A flooring of timber or lightweight metal panels is usually laid across a pontoon bridge.
Pontoon bridges are especially important during wartime. These bridges are built to replace those that have been destroyed by enemy forces. Special pontoon-laying troops bridge streams with mechanical exactness, even under fire. The soldiers lay the flooring, section by section, fastening it securely to the pontoons. Pontoon bridges are usually of limited strength, though sufficient to carry ordinary road vehicles. Soldiers must break step in crossing them to prevent the swaying of the bridge caused by marching in time.
The importance of pontoon-bridge building was shown in Europe during World War II (1939-1945). Retreating troops blew up many bridges across important rivers. Engineers of pursuing armies built pontoon bridges, permitting troops and mechanized equipment to cross the rivers.
In the United States, pontoons have been used for permanent bridges in places where deep water makes pier construction too expensive. Three large concrete floating bridges have been built in the state of Washington. One of these has the longest floating span in North America. This span stretches 7,518 feet (2,291 meters) across Lake Washington.
