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.

As opposed to land warfare, naval mines are sufficiently large and complex that they are designed by engineers and produced in factories. Improvised explosive devices (IED) are quite common in land warfare, along with land mines that are produced by industry.

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.

Military rationale for mine warfare

Mines have been in use since the American Revolution, if not before. Their use involves a much more complex set of tradeoffs than mine (land warfare). While they can be a threat to civilian shipping, especially modern mines can be made selective to particular and legitimate military targets.

Mine sensing and detonation technology

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. Subsequent mines use influence detonators, which depend on magnetic fields, acoustic signatures, pressure waves in water, or combinations of the three types.

Magnetic influence

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.

Computer-controlled mines with complex sensors

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.

Mine countermeasures

Minehunting, minesweeping, and clearance diving are not mutually exclusive; they complement another.

Passive countermeasures of mines include reducing signatures by which mines detect vessels, and various structural modifications that reduce the damage caused by underwater explosions.

Minehunting

Minehunting uses requires purpose built vessels equipped with mine detection; the minehunter may also neutralize the mine, or mark it for neutralization by minesweepers, divers, weapons fire, or other method. The basic approach uses a purpose-built vessel that produces a minimum of magnetic, acoustic, and pressure effects, and has a range of sensors to detect mines. It also needs precision navigational equipment to mark mines that it has detcted.

Minehunting vessels are making increasing use of unmanned undersea vehicles (UUV),. Multiple UUVs may be use to characterize a potential mine, starting with pairs of low-cost, potentially disposable "scouts" that triangulate the mine's position, and then approach the mine with sensors. A scout may also deliberately destroy the mine by triggering its influence sensors, or detonating an explosive charge against it.

Either the "mother" UUV, a manned minehunting ship, or a mine sensor "sled" towed by a helicopter will use various sensors, appropriate to the sea and sea bottom characteristics, to find mine. High-definition sonar, usually short-range and ultrasonic, is the most common sensor.

Minehunting is preferred to minesweeping when the seabed and sonar conditions are well matched to the available sensors, where pressure mines are expected, and where intelligence indicates that MCM vessels may be targeted. Its major advantages are the speed of clearance and the fact that the MCM vessel does not have to pass over the mine to detect it.

Minesweeping

Minesweeping takes direct physical action against a mine, cutting the cable of moored mines so that they may be detonated with weapons fire, or by using "influence sweeps" that generate the type of signatures that detonate the mine. It is preferred to initial minehunting when the presence of moored mines is known, environmental conditions will limit the capability of minehunting sensors or in very shallow water. Minesweepers need not be purpose-built, but vessels with small signatures are preferred, or sweeps operated by UUVs or helicopters.