8"/55 caliber gun

8"/55 caliber naval gun
No. 2 turret of USS New Orleans (CA-32) following a Japanese torpedo-initiated explosion of the forward magazine during the Battle of Tassafaronga on 30 November 1942.
Type	Naval gun Coastal defence
Service history
In service	1925–1975
Used by	United States
Wars	World War II Korean War Vietnam War
Production history
Variants	Mk 9, Mk 12, Mk 14, Mk 15, Mk 16
Specifications
Barrel length	440 inches (11 m) bore (55 calibers)
Shell	335 pounds (152 kg)[1]A.P. 260 pounds (118 kg)[2] H.E.
Caliber	8 inches (20 cm)
Muzzle velocity	2,500 feet per second (760 m/s)[1]
Maximum firing range	30,050 yards (27,480 m)[1]

The 8"/55 caliber gun (spoken "eight-inch-fifty-five-caliber") formed the main battery of United States Navy heavy cruisers and two early aircraft carriers. United States naval gun terminology indicates the gun barrel had an internal diameter of 8 inches (203 mm), and the barrel was 55 calibers long (barrel length is 8 inch × 55 = 440 inches or 11 meters).^[3]

Compare the rounded roofs of early Mark 9 twin and triple turrets of USS Salt Lake City (CA-25) and USS Pensacola (CA-24) with the later turrets of USS New Orleans (CA-32) on the right.

Mark 9

These built-up guns weighed about 30 tons including a liner, tube, jacket, and five hoops. A down-swing Welin breech block was closed by compressed air from the gas ejector system. Loading with two silk bags each containing 45-pounds (20 kg) of smokeless powder gave a 260-pound (120 kg) projectile a velocity of 2800 feet per second (850 m/s).^[1] Range was 31,860 yd (29,130 m) at the maximum elevation of 41 degrees.^[1][4]

Mark 12

These simplified built-up guns eliminated hoops to reduce weight to 17 tons. The breech mechanism was similar and loading two silk bags each containing 43-pounds (20 kg) of smokeless powder gave a 335-pound (152 kg) projectile a velocity of 2500 feet per second (760 m/s).^[1] Each gun could fire about four rounds per minute. Maximum range was 30,050 yd (27,480 m) at the maximum elevation of 41 degrees.^[5]

Mark 14

These guns were similar to Mark 9, with the same shell weight and maximum range,^[4] with a smaller chamber and rifling twist increased from 1 in 35 to 1 in 25 in a chromium-plated bore.

Mark 15

These guns were similar to Mark 12, with the same shell weight and maximum range, with the smaller chamber of the Mark 14 gun.^[5] Useful life expectancy was 715 effective full charges (EFC) per liner.

Mark 16

These self-loading guns with lined monobloc construction and vertical sliding breech blocks weighed about 20 tons. Semi-fixed ammunition (projectile and powder case handled separately) with 78 pounds (35 kg) of smokeless powder gave a 335-pound (152 kg) projectile a velocity of 2500 feet per second (760 m/s).^[1] Each gun could fire about ten rounds per minute. Useful life expectancy was 780 EFC per liner. Range was 17 miles (27 kilometers) at the maximum elevation of 41 degrees.^[1][6][7] This gun was modified for the experimental Major Caliber Lightweight Gun.

Coast defense use

The eight twin turrets of Lexington and Saratoga were removed in early 1942 during refits at Pearl Harbor. The turrets were turned over to the United States Army Coast Artillery Corps and remounted as coastal artillery on Oahu. Four two-turret batteries were established at Salt Lake near Aliamanu Crater (Battery Salt Lake, later Battery Burgess),^[8] Wiliwilinui Ridge Military Reservation (Battery Wilridge, later Battery Kirkpatrick),^[9] Opaeula Military Reservation (Battery Opaeula, later Battery Riggs),^[10] and Brodie Camp Military Reservation (Battery Brodie, later Battery George Ricker).^{[11][12][13][14]} After the war, all of the guns and turrets were scrapped in 1948, along with almost all other US coast artillery. One of USS Louisville CA 28 main gun turrets was removed and taken to the Nevada Test Site and converted into a rotating radiation detector, to collect data on nuclear tests: "Mystery in the Desert Is a Mystery No More".

Ships mounting 8"/55 caliber guns

The heavy cruiser USS Helena (CA-75) fires her 8"/55 caliber Mark 15 guns at enemy forces ashore on the Korean Peninsula in August 1950 during the Korean War.

The after turret of the heavy cruiser USS Toledo (CA-133) fires its 8"/55 caliber Mark 15 guns at enemy targets ashore around Incheon, South Korea, on 13 or 14 September 1950 during the bombardment preceding the invasion of Incheon during the Korean War.

The heavy cruiser USS Saint Paul (CA-73) fires her 8"/55 caliber Mark 15 guns at Chinese troops threatening the evacuation of United Nations troops from Hungnam, North Korea, in December 1950 during the Korean War.

The heavy cruiser USS Saint Paul (CA-73)'s forward 8"/55-caliber guns fire at enemy targets ashore in North Vietnam in October 1966 during the Vietnam War.

NOTE to the above table: Turret Structures with two guns which elevated together as an assembly were known as "Twin Turrets." Structures with three guns which elevated together were "Triple Turrets," etc. Turrets where the guns elevated independently of one another were distinguished by different nomenclature. A turret which contained two guns that elevated independently is properly termed a "Two Gun Turret" not a "Twin Turret" and one with three guns a "Three Gun Turret," not a "Triple Turret," etc. All Heavy Cruiser 8"/55cal. gun turrets beginning with the San Francisco Class and there after (Baltimore; Oregon City; and, Des Moines Classes) were "Three Gun Turrets." The same is true of turrets on Light Cruisers and Battleships.

See also

Weapons of comparable role, performance and era

• 203mm/50 Modèle 1924 gun French equivalent
• 20.3 cm SK C/34 Naval gun German equivalent
• 203 mm /53 Italian naval gun Italian equivalent
• 20 cm/50 3rd Year Type naval gun Japanese equivalent
• BL 8 inch Mk VIII naval gun UK equivalent
• 8"/55 caliber Mark 71 gun

References

• Campbell, John (1985). Naval Weapons of World War Two. Naval Institute Press. ISBN 0-87021-459-4. 
• Fairfield, A.P. (1921). Naval Ordnance. The Lord Baltimore Press. 

External links

Wikimedia Commons has media related to 8"/55 caliber gun.

American naval weapons of the Second World War
Capital ship main armament	12"/50 caliber Mark 7 14"/45 caliber 14"/50 caliber 16"/45 caliber Mark 1, 5 & 8 16"/45 caliber Mark 6 16"/50 caliber Mark 7
Cruiser main armament	5"/38 caliber 6"/53 caliber 6"/47 caliber Mark 16 8"/55 caliber 12"/50 caliber Mark 8
Secondary armament	5"/38 caliber 5"/51 caliber
Destroyer, destroyer escort and patrol frigate armament	3″/50 caliber QF 4 inch Mark XIX 4"/50 caliber 5"/38 caliber
Submarine guns	3″/50 caliber 4"/50 caliber 5"/25 caliber 5"/51 caliber 6"/53 caliber
Anti-aircraft weapons	20 mm Oerlikon 1.1"/75 caliber QF 1-pounder 40 mm Bofors 3"/23 caliber 3″/50 caliber 5"/25 caliber
Light weapons	.50 caliber machine gun
Torpedoes	21" Mark 8 21" Mark 10 21" Mark 14 21" Mark 15 21" Mark 18
Anti-submarine weapons	Hedgehog Mousetrap Y-gun K-gun