12"/50 caliber Mark 8 gun

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12"/50 caliber Mark 8 gun
USS Guam (CB-2) firing her 12"/50 guns during a training session sometime in 1944–1945.
Type Naval gun
Place of origin Template:US
Service history
In service 1944–1961[1][2]
Used by Alaska class cruisers
Wars World War II
Production history
Manufacturer Naval Gun Factory, Midvale and Bethlehem Steel Corporation, Watervliet Arsenal[1]
Barrel length 612 inches (15.54 m) bore (50 cal)[1]

Caliber 12 inches (304.8 mm)[1]
Rate of fire 2.4–3.0 rounds per minute[1]
Maximum range 38,573 yards (35,271 m)[1]

The 12"/50 caliber gun Mark 8 was a US naval gun mounted on the Alaska-class cruisers.

Initial designs

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 battleship, 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 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 Factory to be finished. The gun was first deployed in 1944 on the first member of the Alaska class, USS Alaska (CB-1).[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".


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°, while the "barrel life" of the guns was 344 shots; when compared to the 16"/50 caliber Mark 7 gun found in the Iowa-class battleships, Alaska-cruisers could fire about 54 more shots.[1][3]

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 bigger) 14"/50 caliber gun.

The previous 12" gun manufactured for the U.S. Navy was the Mark 7 version, which had been designed and installed in the 1912 era Wyoming-class battleships.[1] The Mark 8 was of considerably higher quality; in fact, it "was by far the most powerful weapon of its caliber ever placed in service."[4]

See also


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  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 DiGiulian, Tony. "United States of America 12"/50 Mark 8". Navweaps.com. Retrieved 7 January 2009. 
  2. 1961 is the year the last remaining Alaska-class ship, Guam, was decommissioned.
  3. DiGiulian, Tony (7 February 2008). "United States of America 16"/50 (40.6 cm) Mark 7". Navweaps.com. Retrieved 7 January 2009. 
  4. Dulin, Jr.,Robert O.; Garzke, Jr.; William H. (1976). Battleships: United States Battleships in World War II. Naval Institute Press. p. 190. ISBN 1557-5-0174-2.