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.
Trench knife
Because French industry was working under wartime conditions with numerous material shortages, often using subcontracted labor, even officially sanctioned French Army trench knives tend to vary significantly from knife to knife. The need for knives was so great that already-understrength French Army formations were forced to demobilize hundreds of former cutlery workers so that they could return to their former jobs and begin quantity production of trench knives for the armed forces. As the war went on, newer and more versatile blade-type trench knife patterns such as the double-edged dagger "Couteau Poignard Mle 1916 dit Le Vengeur" began to replace the "French Nail" and earlier stiletto-style trench knives. The French lead in trench knife development was closely followed by the United States, which introduced three successive trench knife models - the M1917, M1918, and Mark I (1918) - all based directly or indirectly upon previous French designs.