6 inch/30 gun

• Name — 6"/30 caliber Mark 1, 2, and 3 • Origin — United States • Type — Naval gun • Is Ranged — YES • Is Artillery — YES • Service — 1885 • Used By — United States Navy • Wars — * Spanish–American War • Philippine–American War • World War I • Designer — Bureau of Ordnance • Design Date — 1883 • Manufacturer — U.S. Naval Gun Factory • Number — * Mark 1: 1 • Mark 2: 20 • Mark 3: 109 • Variants — Mark 1, Mark 2 Mod 1 – Mod 3, Mark 3 Mod 0 – Mod 9 • Weight — * Mark 1: (without breech) • Mark 2: • Length — * Mark 1: • Mark 2: • Mark 3 Mod 0 and Mod 3: • Mark 3 Mod 1: • Mark 3 Mod 2 and Mod 8: • Part Length — * 30 Caliber: bore (30 calibers) • 35 Caliber: bore (35) • 40 Caliber: bore (40) • Cartridge — * naval armor-piercing • Rate — * As commissioned: 0.66 rounds per minute (bag guns) • After 1906: 7.3 rounds per minute (bag guns) • As commissioned: 1.5 rounds per minute (case guns) • After 1906: 7.6 rounds per minute (case guns) • Velocity — * 30 caliber • 35 caliber • 40 caliber • Range — * at 15.3° elevation • at 30.2° elevation • Elevation — * Mark 3: −7° to +12° (early units) • Mark 3: −10° to +12° (later units) • Traverse — −150° to +150°

The 6-inch/30 caliber Mark 1, 2, and 3 guns were developed before the Spanish–American War and still used black powder or brown powder, in later years they were not considered strong enough to withstand the higher chamber pressures generated by the newer smokeless powder adopted around 1898 and were obsolete before the start of World War I. The Mark 1, gun No. 1, was constructed of tube, jacket, 16 hoops, an elevating band, and integral trunnions with a screwed-on muzzle bell. The Mark 2 also trunnioned with the Mark 2 Mod 1, which had only 10 hoops, a jacket, and a chamber liner; the Mod 2 was the same, but with a full-length liner. All Mark 1 and Mark 2 guns were constructed to a length of 30 calibers. In 1895, all Mark 2s were ordered to be converted to rapid-fire, fixed ammunition. This was done in 1898–1902 with gun No. 2 being delivered in November 1898 for use in Atlanta. The Mark 3 was trunnioned as the Mark 1 and Mark 2, but was built in three different caliber lengths, 30, 35, and 40, in eight different Mods, Mod 0 – Mod 6, and Mods 8 and 9. Mod 0 was 30-caliber, with Mod 1 being 35-caliber. All 30- and 35-caliber Mods had a liner, 10 hoops, and a jacket. Mod 2 was a 40 caliber with only eight hoops. Mod 3 was again 30 caliber but introduced the use of case (semi-fixed) ammunition. The Mod 4 was experimental in that it eliminated the trunnions and used a threaded sleeve. Mod 5s were reworked, enabling Mod 1s to handle case ammunition. As with the Mod 5, the Mod 6 was a Mod 2 reworked to handle case ammunition. The Mod 7 was skipped, and no drawings exist for this Mod. The Mod 8 was another Mod 2 rework, this time removing the trunnions and replacing them with a threaded sleeve. The last Mod was Mod 9, using a Mod 3 gun and a full-length liner.

• Ship — Gun Installed — Gun Mount • Dolphin — Mark 1: 6"/30 caliber — Mark 1: 1 × shifting pivot • Atlanta — Mark 2: 6"/30 caliber — Mark 2: 6 × muzzle pivot mount • Boston — Mark 2: 6"/30 caliber — Mark 2: 6 × muzzle pivot mount • Chicago — Mark 2: 6"/30 caliber — Mark 2: 8 × muzzle pivot mount • Maine — Mark 3: 6"/30 caliber — Mark 3: 6 × central-pivot • Texas — * Mark 3: 4 × 6"/30 caliber * Mark 3: 2 × 6"/35 caliber — Mark 4: 6 × central-pivot w/single-piece slide • Newark — * Mark 3: 6"/30 caliber (as built) * Mark 3: 6"/40 caliber (refit 1901–1902) — Mark 3: 12 × central-pivot • Charleston — Mark 3: 6"/30 caliber — Mark 3: 6 × central-pivot • Baltimore — Mark 3: 6"/30 caliber — Mark 3: 6 × central-pivot • Philadelphia — Mark 3: 6"/30 caliber — Mark 3: 12 × central-pivot • Columbia — Mark 3: 6"/40 caliber — Mark 3: 2 × central-pivot • Minneapolis — Mark 3: 6"/40 caliber — Mark 3: 2 × central-pivot • Yorktown — Mark 3: 6"/30 caliber — Mark 4: 6 × central-pivot w/single-piece slide • Petrel — Mark 3: 6"/30 caliber — Mark 4: 6 × central-pivot w/single-piece slide • Concord — Mark 3: 6"/30 caliber — Mark 4: 6 × central-pivot w/single-piece slide • Bennington — Mark 3: 6"/30 caliber — Mark 4: 6 × central-pivot w/single-piece slide

At least five guns of this type are preserved: • One gun from Maine (ACR-1) in Washington, DC at the National Museum of the United States Navy. • One gun from Maine (ACR-1) in Portland, Maine at Fort Allen Park. • One gun from Maine (ACR-1) at the city hall in Alpena, Michigan. • Two guns from Concord (PG-3) at the Veterans Memorial Museum, Chehalis, Washington.

• BL 6 inch gun Mk II – VI approximate British equivalent