Shown here here is the Type IXD2 oceangoing boat U178 passing through the lock at Bordeaux towards the U-Boat bunker in the far distance and the nearly completed bunkered lock on the right. The pontoon-like structure towards the far right corner of the lock is a rotating bridge, allowing the road to pass over the lock and through the back of the bunker. Taken from Hitler's U-Boat Bases.
