The 21st Reserve Division fought on the Western Front, participating in the opening German offensive which led to the Allied Great Retreat and ended with the First Battle of the Marne. Thereafter, the division remained in the line in the Champagne region until June 1916. In July 1916, the division entered the Battle of Verdun. It returned to the Champagne in September and then went back to Verdun in December 1916-January 1917. In the Spring of 1917, the division fought in the Second Battle of the Aisne, also known as the Third Battle of Champagne. In November 1917, the division saw action in the tank battle at Cambrai. The division participated in the 1918 German spring offensive. It faced the Allied Hundred Days Offensive, and fought in the Second Battle of the Somme (1918) (also called the Third Battle of the Somme). Allied intelligence rated the division as second class.