They did, well they planned for it anyway. In the event of another conflict, the Maginot Line was supposed to prevent any German advance into France across the Frontier. For diplomatic reasons, the Maginot Line did not extend along the French-Belgian border. To address this inherent weakness, it was planned that British and those French forces not garrisoning the Maginot Line would mass along the Belgian border with France. If Germany attempted to use Belgium as a highway as they intended to in 1914, the Anglo-French forces would advance into Belgium, swinging like a door with the Ardennes Forest as the hinge. The whole strategy relied on the Germans either advancing through Belgium or attacking the Maginot Line head on as it was deemed the Ardennes Forest did not possess the road infrastructure to support a large scale offensive through the region.