In World War I in 1914, the 21st Infantry Division fought in the Allied Great Retreat, including the First Battle of the Marne, and in the Race to the Sea. In 1916, it saw action in the Battle of Verdun and the Battle of the Somme. In 1917, it fought in the Second Battle of the Aisne. It served in the German 1918 Spring Offensive, including the Second Battle of the Somme. Allied intelligence rated the division as first class.