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.
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 10–11 May, XIX Panzer Corps engaged the two cavalry divisions of the Second Army, surprised them with a far larger force than expected and forced the French 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The Ninth Army to the north had also sent its two cavalry divisions forward, which were withdrawn on 12 May, before they met German troops. Corap needed the cavalry divisions to reinforce the defences on the Meuse, because some of its 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 Meuse.
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, 135 RAF day bombers being reduced to 72 operational aircraft by 12 May.[6]
Against the plan, Guderian and the other panzer generals, Rommel among them, disobeyed orders and quickly advanced to the English Channel.
The panzer forces captured Abbeville and fought the Battle of Boulogne and the Siege of Calais, only temporarily being halted by Hitler on 17, 22 and 24 May, then advancing again and fighting the Battle of Dunkirk. The effects of the Manstein Plan were devastating for the Allied armies, as they were encircled by Army Groups A and B, leading to Operation Dynamo, the evacuation from Dunkirk.
The losses in the north and resulting lack of mobile reserves led to the defeat of the remaining French and British forces and the fall of France.[