After the invasion of the Soviet Union in June 1941, the OKH became primarily responsible for planning operations in that theatre, while the Armed Forces High Command ("Oberkommando der Wehrmacht", or OKW) was responsible for other theatres. Halder was replaced as Chief of the General Staff in September 1942 by General Kurt Zeitzler. Heusinger remained chief of the "Operationsabteilung" and was promoted to Generalleutnant on 1 January 1943. In June 1944, Zeitzler suffered a nervous breakdown and abandoned his post, and on 10 June, Heusinger temporarily assumed his office as Chief of the General Staff of the Army. In this capacity, he attended the meeting at Adolf Hitler's Wolf's Lair on 20 July 1944, and was standing next to Hitler when the bomb planted by Claus von Stauffenberg exploded.