Marchovelette: the first offensive
Profiting from the experience of the battles of Liège, the Germans chose to use heavy artillery from the beginning of the attack on Namur. The forts suffered the bombing of shells whose calibre, 305 and 420 mm, was twice that which they could withstand. At the time of the forts' construction, the greatest calibre that could be used in battle was 21 mm. General Brialmont, who conceived the forts, hadn't envisaged that greater calibre mortars could be transported onto the battle fields.
Moreover, the Germans concentrated their attack on a perimeter, that of the Cognelée and Marchovelette forts, rather than launching a general offensive, which reinforced the efficacy of their action. After only three days, the fortified position of Namur was in the hands of the enemy.