For technical clearance, the Neger was not really a submarine, as they could not dive. They simply swam close on the water surface. Besides this technical fact, they were very dangerous for the soldiers, a lot of them never returned.
One of the first mission happened at the Anzio beaches in Italy where they should destroy the American / British landing fleet.
The submarines are 3D printed and painted in black. Most pictures show this color for them.
The rest of the Diorama is really handmade.