 The French assumption was always that Germany would not go to war without conscription, which would allow the German Army to take advantage of the "Reich"s numerical superiority.Without the natural defensive barrier provided by the Rhine River, French generals argued that France needed a new defensive barrier made of concrete and steel to replace it.The power of properly dug-in defensive trenches had been amply demonstrated during World War I, when a few soldiers manning a single machine gun post could kill hundreds of the enemy in the open and therefore building a massive defensive line with subterranean concrete shelters was the most rational use of French manpower.