The partially collapsed structure is what remains of Fort Huger's shell house, a long enclosure covered with a thick layer of earth that served as storage shelter for the fort's ammunition supply, specifically exploding shells charged with black powder and armed with a timed fuse. Solid iron shot coated with a protective layer of coal tar could be safely stored outside next to the cannons, but the more sensitive exploding shells had to be protected from adverse weather because wet fuses could not function properly. Nearby are the scattered brick remnants of Fort Huger's shot furnace, one of several structures blown up by the retreating Confederates as reported in period dispatches. Such ovens were standard in seacoast defense forts. Solid iron cannonballs, mostly of the 32-pound size, were heated over a coal fire within this furnace, then loaded onto a metal cradle and quickly placed into the muzzle of charged cannon. This dangerous and delicate procedure, combined with accurate aim and firing, could set wooden-hulled ships on fire, but it was not successful against ironclads such as the Galena.