As the BEF withdrew through Belgium into northern France , fewer supply troops were needed as the lines of communication shortened .
Within a few days , the panzers achieved a breakthrough against the centre of the French front near Sedan and drove westwards down the Somme river valley .
As the BEF withdrew through Belgium into northern French , fewer supply troops were needed as the lines of communication shortened .
Within a few days , the panzers achieved a breakthrough against the centre of the French front near Sedan and drove westwards down the Somme river valley .