The Manstein Plan is one of the names used to describe the war plan of the German Army during the Battle of France in 1940. The original invasion plan was an awkward compromise devised by General Franz Halder, the chief of Oberkommando des Heeres staff (OKH, Army High Command) that satisfied no one. In the final version of the plan, the main effort of the German invasion was made against the Ardennes, which by coincidence, was the weakest part of the Allied line, where the defence was left to second-rate French divisions in the Second Army and the Ninth Army, on the assumption that the difficulty of moving masses of men and equipment would give the French plenty of time to send reinforcements if the area was attacked. The Seventh Army, which had been the most powerful part of the French strategic reserve, had been committed to a rush through Belgium to join with the Dutch Army to the north, in the Breda variant of Plan D, the Allied deployment plan.
The Manstein plan has often been called Operation Sichelschnitt, a transliteration of "sickle cut", a catchy expression used after the events by Winston Churchill. After the war, German generals adopted the term, which led to a misunderstanding that this was the official name of the plan or at least of the attack by Army Group A. The German name was Aufmarschanweisung N°4, Fall Gelb (Campaign Instruction No 4, Case Yellow) issued on 24 February 1940 and the manoeuvre through the Ardennes had no name. Five panzer divisions of Panzergruppe von Kleist advanced through the Ardennes, XIX Panzer Corps with three panzer divisions on the southern flank towards Sedan, against the French Second Army and the XLI Panzer Corps with two panzer divisions on the northern flank, towards Monthermé, against the French Ninth Army (General André Corap).[7][b] XV Corps moved through the upper Ardennes towards Dinant, with two panzer divisions, as a flank guard against a counter-attack from the north. From 10 to 11 May, XIX Panzer Corps engaged the two cavalry divisions of the Second Army, surprised them with a far larger force than expected and forced them back. The Ninth Army to the north had also sent its two cavalry divisions forward, which were withdrawn on 12 May, before they met German troops.[8]
Corap needed the cavalry divisions to reinforce the defences on the Meuse, because some of the Ninth Army infantry had not arrived. The most advanced German units reached the Meuse in the afternoon; local French commanders thought that the German parties were far ahead of the main body and would wait for it, before trying to cross the river. From 10 May, Allied bombers had been sent to raid northern Belgium to delay the German advance, while the First Army moved up but attacks on the bridges at Maastricht had been costly failures (the 135 Advanced Air Striking Force (AASF) day bombers were reduced to 72 operational aircraft by 12 May). The success of the German invasion surprised everyone; the Germans had hardly dared hope for such a result. Most generals had vehemently opposed the plan as being much too risky; even those supporting it had mainly done so out of desperation because the geostrategic position of Germany seemed so hopeless. Two of the most prominent were Hitler and Halder; Hitler had not liked Halder's original plans and had suggested many alternatives, some of them bearing a resemblance to the Manstein Plan, the closest being a proposal made by him on 25 October 1939.
