An armoured vehicle-launched bridge (AVLB) is a combat support vehicle, sometimes regarded as a subtype of military engineering vehicle, designed to assist militaries in rapidly deploying tanks and other armoured fighting vehicles across gap-type obstacles, such as rivers. The AVLB is usually a tracked vehicle converted from a tank chassis to carry a folding metal bridge instead of weapons. The AVLB's job is to allow armoured or infantry units to cross craters, anti-tank ditches, blown bridges, railroad cuts, canals, rivers and ravines, when a river too deep for vehicles to wade through is reached, and no bridge is conveniently located, or sufficiently sturdy, a substantial concern when moving 60-ton tanks.