16"/50 Caliber Mark 7 Gun - Super-heavy Shell

Super-heavy Shell

The Mark 7 gun was originally intended to fire the relatively light 2,240-pound (1,020 kg) Mark 5 armor-piercing shell. However, the shell-handling system for these guns was redesigned to use the "super-heavy" 2,700-pound (1,200 kg) APC (Armor Piercing, Capped) Mark 8 shell before any of the Iowa-class battleships were laid down. The large caliber guns were designed to fire two different 16 in (406 mm) shells: an armor piercing round for anti-ship and anti-structure work, and a high explosive round designed for use against unarmored targets and shore bombardment.

The North Carolina and South Dakota classes used the preceding 16"/45 caliber Mark 6 gun, which could fire the 2,700-pound shell, but with a shorter range. The Mark 6 gun was lighter, which helped both battleship classes to conform to the limits of the Washington Naval Treaty.

The Mark 7 guns and the 2,700-pound projectiles were 25 percent lighter than the 46 cm/45 Type 94 naval guns of the Japanese Yamato-class battleships, but had nearly the same armor penetration ability.

The Mark 8 shells gave the North Carolina, South Dakota, and Iowa classes the second heaviest broadside of all battleship classes, although the North Carolina and South Dakota ships were treaty battleships. Only the Yamato-class super-battleships could throw more weight.

The propellant consists of small cylindrical grains of smokeless powder with an extremely high burning rate. A maximum charge consists of six silk bags, each filled with 110 pounds of propellant.