A marine mine detonated by a mechanism that reacts to quite a few magnetic product, like the metal hull of a ship.
A mine which reacts on magnetized area of a target.
A marine my own that's detonated by a mechanism that detects the nearness of magnetized product (whilst the metallic hull of a ship). A magnetic countertop mine may let the passagw of several boats before detonating.
(nautical) a marine my own that is detonated by a mechanism that reacts to magnetized product (as the metal hull of a ship)