In 1940, Blumentritt—as the Operations Officer of Army Group A (again under von Rundstedt)—took part in the planning (with von Manstein and Henning von Tresckow) and execution of the invasion of France. The plan he helped develop was called "Sichelschnitt" or "Sickle Cut", and was later referred to as the Manstein Plan. The subsequent unmitigated success of the German "Blitzkrieg" in France and the complete collapse of the French defense shocked even the Germans. However, as the German army closed in on complete victory, Blumentritt and Rundstedt ignored conflicting orders from the OKH to advance on the British and French position at Dunkirk, and instead followed Adolf Hitler′s order to halt for three days, consequently allowing the evacuation of the British Forces.