Army Group C was formed from Army Group 2 in Frankfurt on 26 August 1939. It initially commanded all troops on Germany's western front but after the Polish campaign it was reduced to commanding the southern half of the western front, overseeing the frontal breakthrough through the Maginot Line during June 1940. At the end of the battle of France it moved back to Germany then – under the cover name "Section Staff East Prussia" – moved to East Prussia on 20 April 1941.