Naval mine

A naval mine is a self-contained explosive device placed in water or space to damage or destroy ships. Unlike depth charges or missiles, mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel. Naval mines can be used offensively—to hamper enemy shipping movements or lock vessels into a harbor; or defensively—to protect friendly vessels and create "safe" zones.

As military weapons, mines come in many varieties, from simple explosive, through thermonuclear to antimatter and gravitational.