The Mark 7 gun is the main armament on the Iowa class ships and fires two kind of rounds;
a 2,700-pound AP (Armor Piercing) and a 1,900-pound HC (High Capacity) shore bombardment
projectile. They are called 3-gun turrets as opposed to triple turrets, because each gun
is mounted on its own elevation drive. Two turrets are located forward and one aft.
16-inch guns are known as "bag guns" because the propellant charge is contained in bags which are loaded separately from the projectiles. The bags are filled with stacks of pellets which, when ignited by a small pad containing black powder, propels the projectile forward.