During the opening phases of World War I, the 18th Infantry Division participated in the Battle of Liège, the Allied Great Retreat, the First Battle of the Marne, and the First Battle of the Aisne. In 1916, it saw action in the Somme, and in 1917 it was involved in the Battles of Arras and Passchendaele. In 1918, it participated in the German spring offensive and the subsequent Allied counteroffensives, including the Hundred Days Offensive. Allied intelligence rated it a first class division.