8"/45 caliber gun

8"/45 caliber Mark 6
USS Rochester (CA-2), ex-USS New York (ACR-2), forward 8"/45 Mark 12 turret in 1932.
Type	Naval gun Coastal artillery Railway gun
Place of origin	United States
Service history
In service	1906
Used by	United States Navy  United States Army  Hellenic Navy
Wars	World War I Greco-Turkish War World War II
Production history
Designer	Bureau of Ordnance
Designed	1900
Manufacturer	U.S. Naval Gun Factory
Number built	148 (Nos. 108–255)
Variants	Mark 6 Mod 1 – Mod 4
Specifications
Weight	41,518 lb (18,832 kg) (without breech) 41,988 lb (19,045 kg) (with breech)
Length	369 in (9,400 mm)
Barrel length	360 in (9,100 mm) bore (45 calibers)
Shell	260 lb (120 kg) naval armor-piercing 260 lb (120 kg) army AP Mark 20 240 lb (110 kg) army high-explosive M103
Caliber	8 in (203 mm)
Recoil	28.5 in (720 mm) max
Elevation	Marks 12: -7° to +20° Marks 5: −7° to +20° M1A1: −0° to +45°
Traverse	−135° to +135° naval mounts 360° army M1A1 mount
Rate of fire	1 to 2 rounds per minute
Muzzle velocity	2,750 ft/s (840 m/s) naval AP 2,100 ft/s (640 m/s) army AP 2,750 ft/s (840 m/s) army AP (super charge) 2,150 ft/s (660 m/s) army HE 2,840 ft/s (870 m/s) army HE (super charge)
Effective firing range	22,500 yd (20,574 m) at 20.1° elevation 35,300 yd (32,278 m) at 45° elevation (Army RR gun)

The 8"/45 caliber Mark 6 gun (spoken "eight-inch-forty-five--caliber") were used for the secondary batteries of the United States Navy's last pre-dreadnought battleships and refitted in older armored cruisers main batteries.^[1]

Design

The 8-inch (203 mm)/45 caliber gun was developed after the Spanish-American War to use the new smokeless powder that had recently been adopted by the Navy. This gun was much stronger than its predecessor, the 8-inch/40 caliber gun,^[1] which were incapable of handling the new powder. This was shown when the muzzle of one of Colorado's guns blew off on 22 June 1907, during gunnery practice off Shantung.^[2] The Mark 6, gun Nos. 108 – 255, 148 in total, was constructed of tube, jacket, four hoops a locking ring and the liner with a Welin breech block. These were all constructed of nickel steel. There were a tolal of eight different Mods, Mark 6 Mod 0 to Mark 6 Mod 7, with different liners, breech mechanisms, chambers, and rifling being used.^[1][3]

Service history

The guns mounted in the Virginia-class battleships were in an unusual two-level turret with the 8-inch guns on top of the larger 12-inch (305 mm) guns. This arrangement ultimately proved unsuccessful but helped the Navy in the successful development of superfiring turrets later used in the dreadnought South Carolina.^[1][3]

Due to an older 8-inch/40 caliber Mark 5s muzzle blowing off during gunnery practice in Colorado on 22 June 1907, all Mark 5s were removed from service, rebuilt, and placed in reserve. Because of this, all Pennsylvania-class armored cruisers and the armored cruiser New York, were refit with the newer Mark 6 guns.^[2][3]

With the signing of the Washington Naval Treaty, the pre-dreadnoughts still in service were required to be scrapped. This surplussed up to 48 guns, which the Army used for coastal artillery, using new mountings and new lighter, and more streamlined, projectiles.^[1][3]

Naval Service

Coast defense service

8-inch MkVIM3A2 railway gun

Up to 48 of these weapons served as coast defense weapons with the United States Army Coast Artillery Corps in World War II. They were designated "8-inch Navy gun MkVIM3A2". Twenty-four to thirty-two of these weapons were on the M1 railway mounting, divided into four-gun batteries, stationed in Delaware, Los Angeles, and Puget Sound, among other CONUS locations. Sixteen additional weapons were mounted in two-gun batteries in fixed emplacements on the M1 barbette carriage, with some additional batteries not completed. Most of the fixed weapons were in Alaska, Hawaii, and Puerto Rico.^[4]

Surviving Examples

Four weapons of this type survive, all previously used in coast defense:^[5]

• One gun at Fort Miles, Delaware, on M1 railway proof mount (experimentally bored out to 9.12-inch (232 mm)) (was previously at Naval Surface Warfare Center Dahlgren Division, Dahlgren, VA^[6]
• Two 8-inch Guns Mk VI M3A2 (#160L2 & #154L2), Battery 404, Fort Abercrombie, Kodiak, AK
• One 8-inch Gun Mk VI M3A2 (#134L2), Kodiak Airport, Kodiak, AK (gun formerly at Battery 403, Fort J.H. Smith, Kodiak, AK)

Notes

References

External links

Wikimedia Commons has media related to 8"/45 caliber gun.

Bluejackets Manual, 1917, 4th revision: US Navy 14-inch Mark 1 gun