Fall Gelb — the order of 9 May 20:00

After six months of phoney war and twenty-nine successive postponements, Fall Gelb is at last launched. Hitler gives the order on 9 May 1940 at 20:00, in a curt formula: "Fall Gelb, X-Tag = 10.5.1940." That same evening, he leaves Berlin aboard his special train Amerika and reaches, on the morning of 10 May, his advanced headquarters at the Felsennest, near Mönichkirchen, in the Eifel.

The plan adopted is the Sichelschnitt devised by Manstein, which launches three army groups simultaneously. In the north, Fedor von Bock's Heeresgruppe B is to fall on the Netherlands and northern Belgium to draw in the Allies. In the centre, Gerd von Rundstedt's Heeresgruppe A delivers the main blow, breaking through the Ardennes towards Sedan and on to the Channel. In the south, Wilhelm Ritter von Leeb's Heeresgruppe C confines itself to fixing the Maginot Line passively.

The forces engaged are considerable: three million Germans, two thousand five hundred tanks — of which only eight hundred are modern Panzer III and IV models — and five thousand aircraft. Facing them stand two million Allies, namely the British Expeditionary Force, the French army, the Belgians and the Dutch, fielding three thousand six hundred technically superior tanks on the French side, with the B1 bis and the Somua S35, and three thousand aircraft.

At 04:35, the offensive is launched everywhere at once, in near-total operational surprise. From the first hours, Brandenburger commandos seize one hundred and thirty bridges, paratroopers descend on the Netherlands, and the assault on Eben-Emael begins. Hitler must at once set the operational tempo of his Panzers.