Magnetic pistol is the term for the device on a torpedo or naval mine that detects its target by its magnetic field, and triggers the fuse for detonation. A device to detonate a torpedo or mine on contact with a ship or submarine is known as a contact pistol.

A magnetic pistol on a mine will allow the mine to detonate in proximity to a target, rather than actual contact, allowing the mine to cover a larger effective area.

A magnetic pistol on a torpedo allows the torpedo to detonate underneath the ship, instead of upon impact with the side of the ship. As an explosion underneath a ship is contained between water and the ship, far more damage will result to the ship. The explosion will lift the ship out of the water and may break the keel of the ship, splitting it in two. Any hole created by the explosion will be on the bottom, causing more flooding.

A contact pistol on a torpedo will require the torpedo to strike the side of the ship. Any hole created by the explosion will be closer towards the waterline, reducing flooding. The explosion will also dissipate into the air, reducing the damage. If the torpedo is fired too deep, the torpedo will not hit the ship. If the ship has a round or sloping bottom, the torpedo may glance off the bottom and not detonate.