Mine (naval warfare)

In naval warfare, a mine is an explosive device placed in an area of water in which the user wants to establish a barrier, and which will explode due to some physical effect by a passing vessel. In other words, mines are rarely used in an actual battle, but emplaced to attack at some future time. While the term torpedo was used for mines before the 20th century, the more modern usage of "torpedo" is as a self-propelled weapon used in active combat. The definition does blur with some modern, computer-controlled mines that do not themselves explode, but release a homing torpedo to carry out the final attack, most often against submarines.

One of the reasons mines can be especially effective is that they detonate at or below the waterline, letting water into the ship. In contrast, gunfire and aircraft weapons are more likely to create holes into which air flows, although they may destroy the vessel with indirect effects, such as causing fires.

Mines were originally emplaced by ships, sometimes of a specific design called a minelayer. Major modern powers are more likely to drop mines from aircraft or release them from submarines.

The first mines were triggered by direct contact of the target vessel; the usual icon of a mine is a sphere studded with spikes, with detonators at the ends of the spikes. Later mines could detect the magnetic field of a ship and detonate based on that detonation; this made it practical to have even more destructive explosions under the ship. Mine technology has advanced, and modern mines can detect targets in a variety of ways, including the sound or pressure waves created by the vessel; computer-controlled mines can be set to detonate only on recognizing the acoustic signature of a particular target type. They can also be programmed to delay detonation until several ships pass, so that they wait for escorts and mine countermeasures vessels to pass, and then explode against the presumably high-value asset that the escorts guard.