He was called up as a reserve officer on the outbreak of war, transferring to an administrative post (Wirtschaftsstab Ost) assigned to the Armed Forces High Command in Berlin in 1942. In January 1940, he began to work closely with Helmuth James Graf von Moltke, with whom he initiated and led the discussions of the Kreisau Circle, which met very often at Yorck’s home in Berlin-Lichterfelde. Yorck, who took part in all three of the circle’s conferences in Kreisau, supported a coup attempt to be launched with an assassination, unlike his friend Moltke.