Manstein watches his plan — Koblenz, 10 May

Erich von Manstein, 52, was the intellectual architect of the attack through the Ardennes that Heeresgruppe A was executing on this 10 May 1940. After convincing Hitler in February to strike where Halder had wanted to attack in Belgium, Manstein had been transferred in March to command a reserve infantry corps, the XXXVIII. Armeekorps, far from the main action. Halder, irritated by this subordinate whose voice carried too well, had eased him out of the decisive thrust.

At 05:35, Manstein watched the opening moves from Rundstedt's headquarters at Koblenz. It was Guderian, Reinhardt and Hoth — not he — who were carrying out his plan. He noted every movement: seven Panzer divisions concentrated on a 50-mile front, an unprecedented density, supported by the Brandenburger commandos who seized the border crossings by surprise. The overcast sky masked the concentration from French aerial reconnaissance; the Belgian Chasseurs ardennais, falling back, only weakly delayed the column.

The uncertainty was nonetheless total. Everything depended on speed: if Gamelin and Georges understood early enough that the main effort was not in Belgium but at Sedan, they could still regain the initiative. Manstein, sidelined from operational command, reduced to watching his own plan, had to decide how to conduct himself in the hours ahead.