trench warfare. Although trenches were used in ancient and medieval warfare, in the American Civil War, and in the Russo-Japanese War (1904-5), they did not become important until World War I. The introduction of rapid-firing small arms and artillery made the infantry charges of earlier wars virtually impossible, and the war became immobile, with the contenders digging thousands of miles of opposing trenches fronted by barbed wire. To break the stalemate various methods and new weapons were tried; tremendous artillery barrages sought to devastate the enemy and blow a gap in his trenches; trench mortars, hand grenades, poison gas, and tanks were used. It nevertheless remained a war of attrition, with artillery duels and infantry attacks behind creeping artillery barrages. The idea of an uninterrupted line defense held the imagination of the French and German general staffs between the two world wars, and they built lines of field fortifications known as the Maginot Line and the Siegfried Line. The advent of mechanized warfare made it possible to circumvent such defenses, and World War II was a war of movement. However, in the last stages of the Korean war both sides established fortified positions across the Korean peninsula, and a stalemated situation similar to that of World War I came into play.

trench mouth, common term for Vincent's infection, an ulcerative membranous infection of the gums and mouth, by noncontagious infection, associated with a fusiform bacillus and a spirochete. Poor oral hygiene, nutritional deficiencies, insufficient rest, heavy smoking, and debilitating diseases are predisposing factors to the disease. Epidemics often occur in crowded unsanitary environments, and in former years among soldiers in the field, hence the name "trench mouth." In addition to ulcerations on the gums and mouth, which are painful and bleed freely, there are usually foul breath, increased salivation, and difficulty in swallowing and talking. The acute phase of the disease yields to antibiotic treatment and oxygenating mouth rinses, but attention must also be paid to the underlying dental and medical factors.

trench fever: see rickettsia.

trench: see ocean.

Trench, Richard Chenevix, 1807-86, Irish clergyman and author, b. Dublin. He was dean of Westminster, 1856-63, and Protestant archbishop of Dublin, 1863-84. His many theological writings were eclipsed by his works in philology and poetry, which include The Study of Words (1851), English, Past and Present (1855), and Collected Poems (1865).

Marianas trench, Marianas trough, or Marianas deep, elongated depression on the Pacific Ocean floor, 210 mi (338 km) SW of Guam. It is the deepest (35,798.6 ft/10,911.5 m at the Challenger Deep) known depression on the earth's surface. A U.S. navy bathyscape reached its bottom in 1960; a 1995 Japanese probe made what is probably the most accurate measurement of its depth.

Warfare in which the opposing sides attack, counterattack, and defend from sets of trenches dug into the ground. It was developed by Sébastien Le Prestre de Vauban in the 17th century for laying siege to fortresses. Its defensive use was first institutionalized as a tactic during the American Civil War. It reached its highest development in World War I. Little used in World War II, it reappeared in the Iran-Iraq War in the 1980s. A typical construction consisted of two to four parallel trenches, each dug in a zigzag, protected by sandbags, and floored with wooden planks. The parallel trenches were connected by a series of communication trenches dug roughly perpendicular to them. The first row was fronted by barbed wire and contained machine-gun emplacements; the rear trenches housed most of the troops. Increased use of tanks marked the end of trench warfare, since tanks were invulnerable to the machine-gun and rifle fire used by entrenched soldiers.

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or oceanic trench

Any long, narrow, steep-sided depression in the ocean bottom in which maximum oceanic depths (24,000–36,000 ft, or 7,000–11,000 m) occur. The deepest known depression of this kind is the Mariana Trench. Most trenches occur at subduction zones, where one tectonic plate is thrust under another.

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