At the outbreak of World War I, Heckel completed a training as a nurse with the Red Cross. Initially, he attended seriously injured soldiers in a military hospital in Berlin. In March 1915 he was transferred to a paramedic unit in Flanders, which was under the direction of his friend Walter Kaesbach. Kaesbach drew artists and intellectuals into his unit and, by arranging the roster accordingly, enabled them to pursue their artistic work to a certain extent. Heckel made the acquaintance of the painters Max Kaus, Anton Kerschbaumer and Otto Herbig, and of the lawyer and poet from the circle of Stefan George, Ernst Morwitz, who would become his lifelong friend. The unit was stationed in Ostende, where Heckel was on duty until the end of the war in 1918, apart from a short stint in Gent. He was artistically active the whole time.
