Vesuvius carried three 15-inch (38-cm) cast iron pneumatic guns, invented by D. M. Medford and developed by Edmund Zalinski, a retired officer of the United States Army [REF].
The shells fired from the guns were steel or brass casings 7 feet (2 meters) long with the explosive contained in the conical forward part of the casing and spiral vanes on the after part to rotate the projectile.