6-inch/30-caliber gun

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]