Pontoon /(?)/

Pon·toon

Pontoon

n.
  1. A wooden flat-bottomed boat, a metallic cylinder, or a frame covered with canvas, India rubber, etc., forming a portable float, used in building bridges quickly for the passage of troops. (Mil.)
  2. A low, flat vessel, resembling a barge, furnished with cranes, capstans, and other machinery, used in careening ships, raising weights, drawing piles, etc., chiefly in the Mediterranean; a lighter. (Naut.)

Phrases & Compounds
Pontoon bridge
a bridge formed with pontoons.
Pontoon train
the carriages of the pontoons, and the materials they carry for making a pontoon bridge.