page_title: 16"/50 caliber Mark 7 gun
section_title: Mark 8 "Super-heavy" shell
hierarchical_section_title: 16"/50 caliber Mark 7 gun / Mark 8 "Super-heavy" shell
caption_attribution_description: English: 16"/50 gun projectile plus six propellant bags. Display mockup aboard USS Iowa (BB-61) in San Pedro, CA in 2016.
context_page_description: The 16"/50 caliber Mark 7 – United States Naval Gun is the main armament of the Iowa-class battleship and was the planned main armament of the cancelled Montana-class battleship.
context_section_description: 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) APCBC (Armor Piercing, Capped, Ballistic Capped) Mark 8 shell before any of the Iowa-class battleship's keels were laid down. The large-caliber guns were designed to fire two different 16 inch (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 Mark 7 guns and the 2,700-pound projectiles were 19.2 percent lighter than the 46 cm/45 Type 94 naval guns of the Japanese Yamato-class battleships, but had better armor penetration ability at long range. (Sectional density = 6.9 grams per square millimeter for the IJN shell and 7.43 grams per square millimetrer in the USN gun.)
  The North Carolina and South Dakota classes could also fire the 2,700-pound Mark 8 shell, although with a shorter range, using the 16"/45 caliber Mark 6 gun. The Mark 6 gun was lighter than the Mark 7, which helped both battleship classes to conform to the limits of the Washington Naval Treaty.
  The Mark 8 shells gave the North Carolina, South Dakota, and Iowa classes the second heaviest broadside of all battleship classes, even though the North Carolina and South Dakota ships were treaty battleships. Only the Yamato-class super-battleships could throw more weight.
  The D839 propellant (smokeless powder) grain used for full charges issued for this gun was 2 in (51 mm) long, 1 in (25 mm) in diameter and had seven perforations, each 0.060 in (1.5 mm) in diameter with a web thickness range of 0.193 to 0.197 in (4.9 to 5.0 mm) between the perforations and the grain diameter. A maximum charge consisted of six silk bags–hence the term bag gun–each filled with 110 lb (50 kg) of propellant.
caption: 16"/50 gun projectile with six propellant bags (display) aboard USS Iowa (BB-61)
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