In January 1915, one day before he was called up for military service in World War I, he married Rosa Koch. He was posted to the artillery on the western front, where he stayed till the end of the war, taking part in the Battle of Champagne (1915–1916), the Battle of the Somme (1916), the Battle of Arras (1917), the Second Battle of the Aisne (1917), the Battle of Cambrai (1917) (1917), and the Battle of Soissons (1918). For his service, Thälmann received the Iron cross Second Class, the Hanseatic Cross and Wound Badge (twice).