Mine - in warfare, term formerly applied to a system of tunnels dug under an army fortification and ending in a chamber where either explosives were placed to be detonated at the chosen moment or the supports were burned, causing the mine and the wall above it to collapse. Modern mines are encased explosives detonated by contact, magnetic proximity, or electrical impulse.

Land mines, equipped with pressure sensors slightly above or below ground, came into wide use in World War II, particularly in N Africa and Russia and on the Western front. They are of two general types—antipersonnel and antitank; the latter are designed so that lighter objects will not cause them to explode. Mines can now be manufactured to contain an internal clock that deactivates them after a set time period; they are referred to as "smart" mines. Mines whose detonation deactivation is not set are called "dumb" or persistent mines. To prevent magnetic detection, modern land mines have often been encased in plastic rather than metal.

No completely safe way of removing land mines is known. In World War II the United States and Great Britain developed several types of mine-detecting and mine-exploding equipment, but they proved inadequate. Despite technological advances, identification still usually requires an inch by inch probbing of the ground, which carries great risk and cost.

According to UN figures there are approximately 100 million mines laid across the world, with more than twice that amount in stockpiles. Angola is estimated to have 15 million mines; Cambodia, 10 million (which translates to one per citizen); Afghanistan, 10 million; and Bosnia and Croatia, 3 million each. It is most often the world's civilian populations that are injured (20,000 annually) or killed (10,000).

In 1997 an international treaty, now ratified by more than 135 nations, called for signatory nations to end the use, development, acquisition, and stockpiling of land mines and to destroy their current stocks of such mines; the treaty went into effect in 1999. The United States has refused to sign the treaty, arguing that doing so would hinder the country's ability to protect its troops; Russia and China also have not signed. The International Campaign to Ban Landmines, a coalition of more that 1,000 organizations, won the 1997 Nobel Peace Prize for its efforts to bring about the signing of the treaty. In 2004 the U.S. government announced that it would end the use of persistent land mines by 2010 (and before then outside the Korean peninsula).

Naval mines of various types have been used periodically since the 16th cent., but it was not until World War I that they entered into wide use. Modern naval mines, equipped with sonar or magnetic sensors, are laid on the surface of the sea or sometimes anchored below. They fall within two broad classifications—automatic and controlled. The automatic mine, once planted and armed, is activated by the presence of a ship; it is incapable of discriminating between friendly and enemy ships. The controlled mine, in contrast, is connected by electric cable to a shore station and can be disarmed to allow the passage of friendly vessels. For defensive purposes, mines are often placed in secretly charted locations near protected harbors by specially equipped vessels known as minelayers. As an offensive weapon, mines are placed in or near enemy harbors, generally by aircraft or submarine.

Minesweepers are employed as a countermeasure, often with wooden hulls to avoid magnetic mines. Helicopters can explode mines by towing sweeping equipment while traveling at a safe distance above the water. Minesweeping is vital both during and after a conflict, as thousands of active mines may still be floating in shipping lanes. As recently as the mid-1990s naval mines were discovered in the seabed off a popular beach in Malta; they had been laid by the British during World War II to sink German vessels.

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