Ka cika wannan magana: A Janairu 1915, kwana ɗaya kafin a kira shi ya shiga aikin soja a Yaƙin Duniya na I, ya auri Rosa Koch. An tura shi zuwa ga bindigogi a yammacin gaba, inda ya zauna har zuwa karshen yakin, ya shiga cikin
Yaƙin Champagne (1915<unk>1916), Yaƙin Somme (1916), Yaƙin Arras (1917), Yaƙin na biyu na Aisne (1917), Yaƙin Cambrai (1917) (1917), da Yaƙin Soissons (1918). Don hidimarsa, Thälmann ya karɓi Gicciye na Iron Class na Biyu, Gicciye na Hanseatic da Alamar Rauni (sau biyu).