Trench Warfare Trench warfare was at the center of the fighting in World War I. Both sides constructed a network of trenches and dugout shelters and fought from these trenches to wear the enemy down. This photograph snapped by Sergeant Leon H. Caverly on March 22, 1918, shows Red Cross workers in a trench caring for a wounded American soldier.

Sgt. Leon H. Caverly/Topical Press Agency/Getty Images