When later during the German assault upon Verdun in February 1916 , it proved less effective , as the newer construction of this fort , consisting of concrete reinforced with steel , could mostly withstand the large semi-armour-piercing shells of the Berthas .
When used later during the German assault upon Verdun in February 1916 , however , it proved less effective , as the fort , made of concrete reinforced with steel , could mostly withstand the large semi-armour-piercing shells of the Berthas .