In World War I, the division initially served on the Eastern Front, seeing action at the battles of Stallupönen, Gumbinnen, and Tannenberg, and the First Battle of the Masurian Lakes. The division then fought in the Battle of Łódź and in the Gorlice–Tarnów Offensive of 1915. In March 1916, the 1st Infantry Division was transferred to the Western Front. One month later, it entered the Battle of Verdun. After several months' hard fighting around Fort Vaux, the division was withdrawn from the line and returned to the Eastern Front, where it arrived in August 1916. It then participated in the invasion of Romania, which had entered the war in 1916 on the Allied side. The division returned to Verdun at the end of 1917. In 1918, it took part in the German spring offensive, which the Germans referred to as the "Kaiserschlacht", the Second Battle of the Marne, and the Battle of the Hindenburg Line.