16"/45 caliber Mark 6 gun
|16"/45 caliber gun|
Battleship armament: 16"/45 caliber guns aboard the battleship USS South Dakota (BB-57).
|Place of origin||United States|
|Used by||US Navy|
|Wars||World War II|
|Weight||192,310 pounds (87,230 kg)|
|Length||642.5 inches (16.32 m)|
|Barrel length||720 inches (18 m) bore (45 calibres)|
|Caliber||16-inch (41 cm)|
|Recoil||48-inch (120 cm)|
|Elevation||-2 to 45 degrees|
|Traverse||-150 to 150 degrees|
|Rate of fire||2 rpm|
|Muzzle velocity||AP - 2,300 feet per second (700 m/s), HC - 2,635 feet per second (803 m/s)|
|Maximum range||40,180 yards (36,740 m)|
The 16"/45 caliber Mark 6 gun was a naval gun designed in 1936 by the United States Navy for their Treaty battleships. It was first introduced in 1941 aboard their North Carolina-class battleships, replacing the originally intended 14"/50 caliber Mark B guns and was also used for the follow up South Dakota class. These battleships carried nine guns in three triple turrets. The gun was an improvement to the 16"/45 caliber guns used aboard the Colorado class, and the predecessor to the 16"/50 caliber Mark 7 gun used aboard the Iowa class.
The 16 in/45 were improved versions of the guns mounted on the Colorado-class battleships, hence the designation of "Mark 6". A major alteration from the older guns was the Mark 6's ability to fire a new 2,700-pound (1,200-kilogram) armor piercing (AP) shell developed by the Bureau of Ordnance. At full charge with a brand-new gun, the heavy shell would be expelled at a muzzle velocity of 2,300 feet per second (701 m/s); at a reduced charge, the same shell would be fired at 1,800 f/s (549 m/s).
Barrel life—the approximate number of rounds a gun could fire before needing to be relined or replaced—was 395 shells when using AP, although if only practice shots were used this figure was significantly higher: 2,860. By comparison, the 12"/50 caliber Mark 8 gun of the Alaska large cruisers had a barrel life of 344 shots, while the 16"/50 caliber Mark 7 gun found in the Iowa-class battleships could fire off 290 shots.
Turning at 4 degrees a second, each turret could train to 150 degrees on either side of the ship. The guns could be elevated to a maximum inclination of 45 degrees; turrets one and three could depress to −2 degrees, but due to its superfiring position, the guns on turret two could only depress to 0 degrees.
Each gun was 736 inches (18,700 mm) long overall; its bore and rifling length were 720-inch (18,000 mm) and 616.9-inch (15,670 mm), respectively. Maximum range with the heavy AP shell was obtained at an inclination of 45 degrees: 36,900 yards (21.0 mi; 33.7 km). At the same elevation a lighter 1,900-pound (860-kilogram) high capacity (HC) shell would travel 40,180 yards (22.83 miles; 36.74 kilometres). The guns weighed 192,310 lb (87,230 kg; 86 long tons) not including the breech; the turrets weighed slightly over 3,100,000 lb (1,410,000 kg; 1400 long tons).
When firing the same shell, the 16 in/45 Mark 6 had a slight advantage over the 16 in/50 Mark 7 when hitting deck armor—a shell from a 45 cal gun would be slower, meaning that it would have a steeper trajectory as it descended. At 35,000 yards (20 miles; 32 kilometres), a shell from a 45 cal would strike a ship at an angle of 45.2 degrees, as opposed to 36 degrees with the 50 cal.
The Mark 6 and 7 guns were 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-inch (410 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 8 shells gave the North Carolina, South Dakota, and Iowa classes the second heaviest broadside of all battleship classes, despite the fact that the North Carolina and South Dakota ships were treaty battleships. Only the Yamato-class super dreadnoughts could throw more weight. The Mark 6's disadvantage relative to other contemporary battleship classes was its comparatively shorter range.
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.
This particular 16 inch gun holds two records relating to the United States' World War II combat history.
In the first instance, as the primary armament of USS Washington (BB-56) these guns were employed against the Imperial Japanese Navy's Kirishima during the Naval battle of Guadalcanal; this has been cited by historians as the only instance in World War II in which one American battleship actually sank an enemy battleship. With the aid of a fire control computer—in this case the Ford Instrument Company Mark 8 Range Keeper analog computer used to direct the fire from the battleship's guns, taking into account several factors such as the speed of the targeted ship, the time it takes for a projectile to travel, and air resistance to the shells fired at a target. This gave the US Navy a major advantage in the Pacific War, as the Japanese did not develop radar or automated fire control to the level of the US Navy. Washington was able to track and fire at targets at a greater range and with increased accuracy, as was demonstrated in November 1942 when she engaged Kirishima at a range of 18,500 yards (16,900 m) at night. Using her nine 16"/45 caliber Mark 6 guns Washington fired 45 rounds of 16" AP shells and scored at least nine heavy caliber hits that critically damaged the Kirishima and led to her scuttling.
In the second instance, the battleship USS Massachusetts (BB-59) employed these 16"/45 caliber guns as her primary armament, and she is believed to have to fired the United States' first and last 16 inch shells of World War II; the first use occurring 8 November 1942 during the Naval Battle of Casablanca, the last being 9 August 1945 off the coast of Hamamatsu, Japan. Furthermore, at Casablanca, this was the only time in the European theater that a fast battleship of the US Navy fired her guns in anger. That was also the only instance of a US battleship firing against Axis ships in Europe, when Massachusetts struck the French battleship Jean Bart.
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- This article includes text from the public domain Dictionary of American Naval Fighting Ships. The entry can be found here.
- Garzke, William H.; Dulin, Robert O. (1980). Battleships: Allied Battleships in World War II. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-100-5. OCLC 6355577.
- USS Massachusetts (BB-59). Turner Publishing Company. 1997. ISBN 1563112639. OCLC 38874740.