A form of fighting conducted from long, narrow ditches in which troops stood and were sheltered from the enemy’s fire. At the beginning of World War I the belief that victory came from mass infantry charges dominated military thinking in spite of the introduction of rapid‐firing small arms and artillery. After the first Battle of the Marne thousands of miles of parallel trenches were dug along the Western Front, linked by intricate systems of communication trenches and protected by barbed wire. With such trenches stretching from the North Sea to Switzerland, a stalemate existed and to break it various new weapons were introduced, including hand‐grenades, poison gas, trench mortars, and artillery barrages. Consequently casualties hitherto undreamed of followed every mass infantry attack. Not until 1918, with an improved version of the tank (invented in 1915), was it possible to advance across the trenches. World War II by contrast was a war of movement with no comparable trench fighting. Slit trenches, manned by two or three machine gunners, replaced them. In the Korean War and in Vietnam fortified bunkers were used. Trench warfare was used by the protagonists in the Iran‐Iraq War of 1980–88.