mine, in industry: see mining.

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 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. More than 150 nations are now parties to the treaty. 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 nongovernmental 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.

land mine: see mine, in warfare.

United Mine Workers of America (UMW), international labor union formed (1890) by the amalgamation of the National Progressive Union (organized 1888) and the mine locals under the Knights of Labor. It is an industrial union, including all workers in the coal industry. The lack of continuity of employment, the prevalence of company-owned towns, and the extreme occupational hazards have led to numerous strikes and constant efforts to improve conditions by collective bargaining.

Earlier unions of miners in the United States had been the American Miners' Association (founded 1860); the Miners' National Association of the United States of America (founded 1873); the Ohio Miners' Amalgamated Association (founded 1882), later to become (1883) the Amalgamated Association of Miners of the United States; and the National Federation of Miners and Mine Workers (founded 1885). The newly formed UMW affiliated with the American Federation of Labor (AFL). The UMW strengthened its position in 1894 and 1897 by successful strikes, and in 1898, under the leadership of John Mitchell, the fight for an 8-hour workday was won. A no-strike pledge was kept during World War I, but strikes in 1919-20 led to the establishment by the U.S. government of the Bituminous Coal Commission, which awarded the miners a substantial wage increase. In 1920 the anthracite operators recognized the UMW as a bargaining body.

John L. Lewis became president of the union in 1920, and under his militant leadership most of the union's aims were accomplished, including a health and welfare fund assuring a pension of $100 per month to all miners over 62. The UMW was a leader in the formation (1935) of the Committee for Industrial Organization (later the Congress of Industrial Organizations, or CIO) and was expelled from the AFL in 1937. In 1942, however, the UMW withdrew from the CIO. A strike (1943) during World War II brought about governmental seizure of the mines. Strikes in 1945-47, although successful, cost both Lewis and the union heavy fines for violation of the injunction barring the union from striking. The UMW was readmitted to the AFL in Jan., 1946, but was again disaffiliated in 1947, when Lewis refused to sign the non-Communist affidavit required by the Taft-Hartley Labor Act. Lewis resigned as union president in 1959, and his place was taken in 1960 by Thomas Kennedy, long a vice president of the UMW.

Upon the death of Kennedy, W. A. (Tony) Boyle was elected (1963) president. Throughout the 1960s, Boyle was increasingly criticized by a portion of the rank and file membership. Dissidents rallied to the campaign of Joseph A. Yablonski in 1969, but Yablonski lost to Boyle. A few weeks later Yablonski was murdered. In 1972, Boyle and other top union officials were convicted of making illegal political contributions with union funds. In the same year a federal judge invalidated the 1969 election, and Arnold Miller, a Yablonski supporter, defeated Boyle for the presidency. Miller immediately set about reforming the union by replacing Boyle appointees, stopping Boyle's pension, and reducing the salaries of union officials. In 1974 Boyle, charged with having ordered Yablonski's killing, was convicted of murder.

Since World War II, automation, the popularity of other energy sources, and the establishment of nonunion mining operations have produced a long-term decline in the union's power. Richard Trumka became head of the union in 1982, and in 1989 the UMW reentered the AFL-CIO. When Trumka became secretary-treasurer of the AFL-CIO in 1995, Cecil E. Roberts, Jr., succeeded him as UMW president. In 1998 the UMW had about 240,000 members, far below the half million members it had in 1946; with the reduction in U.S. mining activities, however, the UMW represents about 42% of all employed miners.

U.S. labour union. Founded in 1890, the UMWA grew rapidly under the leadership of John Mitchell (president 1898–1908) despite determined opposition from coal-mine operators. By 1920, when John L. Lewis took over, the union had half a million members. Lewis capitalized on the pro-labour climate of the New Deal and led numerous strikes to win fair pay, safe working conditions, and benefits. The UMWA was a mainstay of the Congress of Industrial Organizations (see AFL-CIO) in its early years, but Lewis withdrew the union from the CIO in 1942. Unaffiliated for decades, the UMWA finally joined the AFL-CIO in 1989. The UMWA's importance declined in the later 20th century with the waning of the labour movement and the rise of alternative sources of fuel, and by the 1990s it had fewer than 200,000 members.

Learn more about United Mine Workers of America (UMWA) with a free trial on Britannica.com.