The Small Box Girder bridge (SBG) was a small assault bridge that could be used to span gaps of up to 30 feet. The design had been formally adopted by the British Army in 1932.

The concept was copied by many countries including Germany and U.S.A.

This is the lengthened, longer version of the SBG that is mounted on the Churchill AVRE. This version has the ramps on both ends and a lengthening section in the middle.