Remains of a war
Unterseeboot is the name given to German submersibles and submarines since the First World War. People were terribly afraid of these formidable weapons during the war. Some really hard battles happened in the depths of the sea.
The German submarines reached a high degree of technical development and attack capacity. They have built various models of submarines, and each one had a symbol of its flotilla, crew, or the ship itself drawn on its sail. There is a lot of history down there.