6-inch/30-caliber gun

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, 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.^[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 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.^[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