12"/50 caliber Mark 8 gun

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12"/50 caliber Mark 8 gun
USS Guam (CB-2) firing main battery, 1944-45.jpg
USS Guam firing her 12"/50 guns during a training session sometime in 1944–1945.
TypeNaval gun
Place of originUnited States
Service history
In service1944–1961[1][2]
Used byAlaska-class cruisers
WarsWorld War II
Production history
ManufacturerNaval Gun Factory, Midvale and Bethlehem Steel Corporation, Watervliet Arsenal[1]
Barrel length51 feet (15.54 m) bore (50 cal)[1]

Shell1,140 pounds (520 kg)
Caliber12 inches (304.8 mm)[1]
Rate of fire2.4–3.0 rounds per minute[1]
Maximum firing range38,573 yards (35,271 m)[1]

The 12"/50 caliber gun Mark 8 was a US naval gun mounted on the Alaska-class cruisers. The gun, like the "large cruiser" that mounted it, was intended to fill the gap between US "heavy cruisers" (6-8") and later US battleships (14-16").

Design and production[edit]

The gun was designed in 1939, and a prototype was tested in 1942. Unlike previous guns, such as the 16"/45 caliber guns used on the North Carolina class, which were completely made and assembled at the Naval Gun Factory in Washington D.C., the forgings for the Mark 8 were manufactured at the Midvale and Bethlehem Steel Corporation. They were then sent to the Naval Gun Factory for processing, which was followed by a trip to Watervliet Arsenal until they were 65% complete. Finally, the built-up guns were sent back to the Naval Gun Factory to be finished.

The gun was first deployed in 1944, on the lead ship of the Alaska class, USS Alaska.[1] The two Alaska-class ships each had nine Mark 8 guns mounted in three triple (3-gun) turrets, with two turrets forward and one aft, a configuration known as "2-A-1". Only two vessels of the class were completed, making them the only applications of the Mark 8 12"/50 caliber gun.


The Mark 8 weighed 121,856 pounds (55,273 kg) including the breech and was capable of an average rate of fire of 2.4–3 rounds a minute. It could throw a 1,140 lb. (517.093 kg) Mark 18 armor-piercing shell 38,573 yards (35,271 meters) at an elevation of 45°.[1][3] The previous 12" gun manufactured for the U.S. Navy was the Mark 7 version, used in the World War I era Wyoming-class battleships,[1] could only throw an 870-pound (390 kg) shell 24,000 yards (21,946 m), at an elevation of 15°[4] The Mark 8's significant improvement in firing weight and range over the Mark 7 gave it the honor of "by far the most powerful weapon of its caliber ever placed in service."[5] In fact, as a result of the decision to fire "super heavy" armor-piercing projectiles, the Mark 8's deck plate penetration was better and the side belt armor penetration equal to the older (but larger) 14"/50 caliber gun.

The barrel life of the Mark 8 guns was 344 shots, which was 54 more shots than the 16"/50 caliber Mark 7 gun found in the Iowa-class battleships.[1][3]

See also[edit]


  1. ^ a b c d e f g h i j DiGiulian, Tony. "United States of America 12"/50 Mark 8". Navweaps.com. Archived from the original on 7 January 2009. Retrieved 7 January 2009.
  2. ^ 1961 is the year the last remaining Alaska-class ship, Guam, was decommissioned.
  3. ^ a b DiGiulian, Tony (7 February 2008). "United States of America 16"/50 (40.6 cm) Mark 7". Navweaps.com. Archived from the original on 7 January 2009. Retrieved 7 January 2009.
  4. ^ DiGiulian, Tony. "United States of America 12"/50 Mark 7". Navweaps.com. Archived from the original on 30 June 2011. Retrieved 2011-07-21.
  5. ^ Dulin, Jr. Robert O.; Garzke, Jr. William H. (1976). Battleships: United States Battleships in World War II. Naval Institute Press. p. 190. ISBN 1-55750-174-2. Retrieved 11 January 2009.

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