Sgt. Ross F. Gray carried a satchel charge though a minefield while under heavy Japanese fire. The explosive weighed 24 pounds and left no room for a rifle. He went in unarmed anyway. Behind him, three Marines provided cover. Ahead, a fortified Japanese bunker anchored one end of a network of gun emplacements that had stopped his platoon cold on Feb. 21, 1945, two days into the bloodiest battle in Marine Corps history. Gray had already mapped a route through the field on foot, under fire,