A flat-bottomed boat, whose frame of wood is covered and lined with tin, or covered with copper; used in forming bridges over rivers for armies.

A lighter; a low flat vessel resembling a barge, furnished with cranes, capstans and other machinery; used in careening ships, chiefly in the Mediterranean. Pontoon-bridge, is a bridge formed with pontoons, anchored or made fast in two lines, about five feet asunder. Pontoon-Carriage, is made with two wheels only, and two long side pieces, whose fore ends are supported by timbers.