Sorge enlisted in the Imperial German Army in October 1914, shortly after the outbreak of World War I. At 18, he was posted to a field artillery battalion with the 3rd Guards Division. He served on the Western Front and was severely wounded there in March 1916. Shrapnel severed three of his fingers and broke both his legs, causing a lifelong limp. He was promoted to the rank of corporal, received the Iron Cross and was later medically discharged. While fighting in the war, Sorge, who had started out in 1914 as a right-wing nationalist, became disillusioned by what he called the "meaninglessness" of the war and moved to the left.