concrete here, with a machine gun nest inside. this machine gun is clearly cited right down to the beach so they had a clear view that the soldiers were coming ashore, and this is what the allied troops had to contend with. >> you can see in the sea behind you, the wreckage of what was called mulberry harbor, the british engineers, american engineers came in and basically made a landing area for all of that equipment that was going to come in for the days and days and days after that successful landing, and you can still see it there rotting in the ocean as a remembrance of the engineering feat that was that morning. >> that's absolutely right. these are big concrete shells that were built over in england, and floated across the channel. part of the meticulous planning that went on, floating across the channel and sunk here to be a break water for the other parts of the mulberry harbor, which were what they call the whales, these were metal