Gamelin and the defensive posture

As commander-in-chief of the French armies, General Gamelin defined, during the Phoney War, the doctrine that would govern the coming battle. French military thinking remained deeply marked by the bloodletting of 1914–1918 and by the 1930s debates on the use of the tank and mobile warfare, which set advocates of caution against proponents of a more mobile army.

Gamelin had to arbitrate between several conceptions. To rely on the Maginot Line and a planned manoeuvre into Belgium, confident in the solidity of the front and the wearing-down of the adversary. To adopt a more offensive and mobile posture, concentrating the armour as advocated by de Gaulle or, on their side, by German theorists. Or to redeploy the effort towards the Ardennes hinge, that wooded massif judged to be under little threat.

The doctrinal choice was decisive: it determined the use of tanks (dispersed in support of the infantry, or concentrated as a manoeuvre mass), the flexibility of the command and the capacity to react to the unexpected. Caution was reassuring, but risked ceding the initiative to a bolder adversary. How should the supreme commander prepare France for the decisive battle?