Sitzkrieg, France, 1939
Hitler invaded Poland on September 1, 1939, and two days later both England and France were technically at war with Germany. England began preparations to send the British Expeditionary Force to France, and the French mobilized their army, but as the bulk of the German war machine swept into Poland, leaving 46 divisions on the Western Front of which only 11 were combat ready, the British and French sat on their hands. In contrast, France was capable of fielding 100 divisions, supported by 4 from the British, and the Royal Air Force, despite the long-standing myth inspired by Churchill’s oratory, was near parity with the German Luftwaffe. Combined with the French, Allied air power exceeded that of the Germans.
The French did plan to mount an offensive in the Saarland, moving 30 divisions and 40 tank battalions to the border. The movement was planned after French probing operations in September revealed the relative weakness of the German defenses. They occupied some German territory, but plans for a full scale invasion of Germany were deferred when the speed of the Polish collapse was revealed to the French commanders. The slowness of the British deployment to Europe was another factor which caused the French to stop short, though an all-out aerial attack of the sort being conducted in Poland by the Germans would have met little resistance, since 90% of Luftwaffe strength was engaged there. By October, the French had withdrawn behind their fortifications.