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,[2] 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.

With the advent of Blitzkrieg warfare, whole divisions had to advance along with tanks, which were suddenly far out-pacing the speed of infantry soldiers.

The rising weight of armoured vehicles meant that fewer bridges could support these massed crossings.

The only feasible solution to the dilemma posed by the mobility of all-mechanised armed forces was a dedicated platform that could improvise river and obstacle crossings at short notice and in inconvenient locations.

Tracked and armoured, it was capable of operating alongside combat units, crossing rough terrain and advancing in the face of light fire.

Twenty were built, but problems of excessive weight limited the vehicle's effectiveness, and eventually all 20 were converted back to tanks.

A new scissors bridge design was brought out by the British in response to the war, sufficient to support a 24-ton load over 30 ft (9.1 m).

Other vehicles were integral to the bridge themselves, such as the Churchill Ark, wading to the middle of a river or driving up against an obstacle and extending simple ramps in both directions.