During the First World War, Piscator was drafted into the German army, serving in a frontline infantry unit as a Landsturm soldier from the spring of 1915 (and later as a signaller). The experience inspired a hatred of militarism and war that lasted for the rest of his life. He wrote a few bitter poems that were published in 1915 and 1916 in the left-wing Expressionist literary magazine "Die Aktion". In summer 1917, having participated in the battles at Ypres Salient and been in hospital once, he was assigned to a newly established army theatre unit. In November 1918, when the armistice was declared, Piscator participated in the November Revolution, giving a speech in Hasselt at the first meeting of a revolutionary Soldiers' Council (Soviet).