8 inch/45 Mark 6 gun

• Name — 8"/45 caliber Mark 6 • Origin — United States • Type — *Naval gun • Coastal artillery • Railway gun • Is Ranged — YES • Is Artillery — YES • Service — 1906 • Used By — *United States Navy • United States Army * • Wars — *World War I • Greco-Turkish War • World War II • Designer — Bureau of Ordnance • Design Date — 1900 • Manufacturer — U.S. Naval Gun Factory • Number — 148 (Nos. 108–255) • Variants — Mark 6 Mod 1 – Mod 4 • Weight — * (without breech) • (with breech) • Part Length — bore (45 calibers) • Cartridge — * naval armor-piercing • army AP Mark 20 • army high-explosive M103 • Rate — 1 to 2 rounds per minute • Velocity — * naval AP • army AP • army AP (super charge) • army HE • army HE (super charge) • Range — * at 20.1° elevation • at 45° elevation (Army RR gun) • Recoil — 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

The 8 in/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, which were incapable of handling the new powder. This was shown when the muzzle of one of Colorados guns blew off on 22 June 1907, during gunnery practice off Shantung. 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 total of eight different Mods, Mark 6 Mod 0 to Mark 6 Mod 7, with different liners, breech mechanisms, chambers, and rifling being used.

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 in guns. This arrangement ultimately proved unsuccessful but helped the Navy in the successful development of superfiring turrets later used in the dreadnought South Carolina. 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 armored cruisers and the armored cruiser New York, were refit with the newer Mark 6 guns. 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.

• Ship — Gun Installed — Gun Mount • Virginia — Mark 6: 8"/45 caliber — *Mark 12: 2 × twin turrets *Mark 5: 2 × dual-caliber turrets • Nebraska — Mark 6: 8"/45 caliber — *Mark 12: 2 × twin turrets *Mark 5: 2 × dual-caliber turrets • Georgia — Mark 6: 8"/45 caliber — *Mark 12: 2 × twin turrets *Mark 5: 2 × dual-caliber turrets • New Jersey — Mark 6: 8"/45 caliber — *Mark 12: 2 × twin turrets *Mark 5: 2 × dual-caliber turrets • Rhode Island — Mark 6: 8"/45 caliber — *Mark 12: 2 × twin turrets *Mark 5: 2 × dual-caliber turrets • Connecticut — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • Louisiana — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • Vermont — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • Kansas — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • Minnesota — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • New Hampshire — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • Mississippi — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • Idaho — Mark 6: 8"/45 caliber — Mark 12: 4 × twin turrets • New York — Mark 6: 8"/45 caliber — Mark 12: 2 × twin turrets • Pennsylvania — Mark 6: 8"/45 caliber — Mark 12: 2 × twin turrets • West Virginia — Mark 6: 8"/45 caliber — Mark 12: 2 × twin turrets • California — Mark 6: 8"/45 caliber — Mark 12: 2 × twin turrets • Colorado — Mark 6: 8"/45 caliber — Mark 12: 2 × twin turrets • Maryland — Mark 6: 8"/45 caliber — Mark 12: 2 × twin turrets • South Dakota — Mark 6: 8"/45 caliber — Mark 12: 2 × twin turrets

• Illustration — 8-inch Mk.VI M3A2 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 Mk.VI M3A2". 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.

Four weapons of this type survive, all previously used in coast defense: • One gun at Fort Miles, Delaware, on M1 railway proof mount (experimentally bored out to 9.12 in) (was previously at Naval Surface Warfare Center Dahlgren Division, Dahlgren, VA • 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)