Transported and laid by specially-designed U-Boats (submarines), German mines like this could damage or sink ships.

Vertical rails with rollers allowed the mine to slide out the bottom of a tube and sink to the bottom of the sea. The circular base remained on the bottom, while the spherical buoyancy chamber (white) containing the explosive charge (red) rose at the end of a cable to a pre-set depth. Contact "horns" (not installed on this example) broke when struck by a ship's hull, detonating the mine's explosive charge.

Naval Mine, German
CWM 19390002-835