6"/30 caliber Mark 1, 2, and 3
Atlanta, 6-inch/30 caliber gun.
Type	Naval gun
Place of origin	United States
Service history
In service	1885
Used by	United States Navy
Wars	Spanish–American War Philippine–American War World War I
Production history
Designer	Bureau of Ordnance
Designed	1883
Manufacturer	U.S. Naval Gun Factory
No. built	Mark 1: 1 Mark 2: 20 Mark 3: 109
Variants	Mark 1, Mark 2 Mod 1 – Mod 3, Mark 3 Mod 0 – Mod 9
Specifications
Mass	Mark 1: 11,010 lb (4,990 kg) (without breech) Mark 2: 10,430 lb (4,730 kg)
Length	Mark 1: 189.7 in (4,820 mm) Mark 2: 193.53 in (4,916 mm) Mark 3 Mod 0 and Mod 3: 196 in (5,000 mm) Mark 3 Mod 1: 226 in (5,700 mm) Mark 3 Mod 2 and Mod 8: 256 in (6,500 mm)
Barrel length	30 Caliber: 180 in (4,600 mm) bore (30 calibers) 35 Caliber: 210 in (5,300 mm) bore (35) 40 Caliber: 240 in (6,100 mm) bore (40)
Shell	105 lb (48 kg) naval armor-piercing
Caliber	6 in (152 mm)
Elevation	Mark 3: −7° to +12° (early units) Mark 3: −10° to +12° (later units)
Traverse	−150° to +150°
Rate of fire	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)
Muzzle velocity	1,950 ft/s (590 m/s) 30 caliber 2,000 ft/s (610 m/s) 35 caliber 2,150 ft/s (660 m/s) 40 caliber
Effective firing range	9,000 yd (8,200 m) at 15.3° elevation 18,000 yd (16,000 m) at 30.2° elevation

The 6"/30 caliber gun Mark 1 (spoken "six-inch-thirty-caliber") were used for the primary battery of the United States Navy's dispatch vessel Dolphin with the Mark 2 being used in the secondary batteries for its "New Navy" protected cruisers Atlanta, Chicago, and Boston and the Mark 3 used for the primary and secondary batteries in the succeeding early protected cruisers in addition to secondary batteries in the "Second Class Battleships" Maine and Texas.^[1][2]

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.^[1]

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 only having 10 hoops, jacket, and chamber liner and the Mod 2 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.^[1][2]

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 Mod's 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 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 Mod 1s making them capable of handling case ammunition. As with the Mod 5 the Mod 6 were Mod 2s 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 using a threaded sleeve. The last Mod was the Mod 9, using a Mod 3 gun and giving it a full-length liner.^[1][2]

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.^[3]
• 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

• Friedman, Norman (2011). Naval Weapons of World War One. Seaforth Publishing. ISBN 978-1-84832-100-7.
• Hartshorn, Byron (24 February 2015). "Visiting the USS Maine around Washington, DC". Retrieved 19 October 2016.
• "United States of America 6"/30, 6"/35 and 6"/40 (15.2 cm) Marks 1, 2, 3, 4 and 7". Navweaps. 3 May 2015. Retrieved 15 May 2016.

• Bauer, K. Jack; Roberts, Stephen S. (1991). Register of Ships of the U.S. Navy, 1775–1990: Major Combatants. Westport, Connecticut: Greenwood Press. ISBN 0-313-26202-0.
• Friedman, Norman (1984). U.S. Cruisers: An Illustrated Design History. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-718-6.

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