In March 1940, Daladier resigned as prime minister because of his failure to aid Finland's defence during the Winter War, and he was replaced by Paul Reynaud. Daladier remained defence minister, however, and his antipathy to the new prime minister prevented Reynaud from dismissing Maurice Gamelin as Supreme Commander of the French armed forces. As a result of the massive German breakthrough at Sedan, Daladier swapped ministerial offices with Reynaud and became foreign minister while Reynaud became defence minister. Gamelin was finally replaced by Maxime Weygand on 19 May 1940, nine days after the Germans began the Battle of France.