スパルタクス団
He was called up for military service in 1912 which would normally have lasted for two years, but the outbreak of war in August 1914 saw him conscripted into the war-time army. In 1916 he was badly wounded and sent home without his left leg. In 1916/17 he was conscripted to work in a gun factory in Erfurt. Here, in 1917, he joined the newly formed Independent Social Democratic Party of Germany (USPD / "Unabhängige Sozialdemokratische Partei Deutschlands") which had broken away from the mainstream SPD primarily over the existing party's continued support for the war. He also joined the Spartacus league in 1917 or 1918. In January 1918 he played a leading role in the organisation in Erfurt of which took place in much of Germany that month. Membership of the USPD and the closely associated Spartacus League led naturally to the newly emerging Communist Party (KPD), and on 26 December 1918 Gräf was a co-founder of the Erfurt branch.