When the advance of his platoon had been held up by machinegun fire and a request was made for an automatic rifle team to charge the nest, Pvt. Costin was the first to volunteer. Advancing with his team, under terrific fire of enemy artillery, machineguns, and trench mortars, he continued after all his comrades had become casualties and he himself had been seriously wounded. He operated his rifle until he collapsed. His act resulted in the capture of about 100 prisoners and several machineguns. He succumbed from the effects of his wounds shortly after the accomplishment of his heroic deed.