That is an amphibious bridge, or at least part of one. When complete as a vehicle it has several ramps on top of it. It, and several others, enters the water and they join together side by side. Then they deploy their ramps in such a way to link up with each other that they become a bridge so that tanks and other military vehicles can cross a river. I believe that they are German made, but they were certainly used by 28 Amphibious Regt RE stationed at Hameln in Germany in the late 70’s. Difficult to explain, but there is TV footage of them in action and they are very spectacular to see.