Trench warfare
Trench warfare occurred when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage. On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, camouflaged trapping pits, and other obstacles. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.
Henri Mordacq
In August 1914, Mordacq was chief of staff of general Archinard's First Reserve Corps Group in the Eastern Army. When the Germans breached the French lines through Belgium, he asked for a frontline command and became commander of the famous 159th Regiment of Alpine Infantry. He immediately took part in the Battle of the Frontiers and his regiment participated in the ending of the German advance in the Vosges before the First Battle of the Marne led to the Race to the Sea. He then took command of the defence of Arras, the "key to the sea" and again halted the German advance there, which led to the stabilization of the front and the beginning of trench warfare.