12-inch/40-caliber gun

12"/40 caliber Mark 3 and Mark 4
View of Ohio and her forward 12"/40 caliber guns in the Mark 4 turret in 1916.
Type	Naval gun
Place of origin	United States
Service history
In service	1902
Used by	United States Navy
Wars	World War I
Production history
Designer	Bureau of Ordnance
Designed	1899
Manufacturer	U.S. Naval Gun Factory
No. built	Mark 3: 41 (Nos. 15–41, 50–56) Mark 4: 10 (Nos. 49, 58–60, 150–154, 179)
Variants	Mark 3 and Mark 4
Specifications
Mass	116,480 lb (52,830 kg) (with breech) 114,960 lb (52,140 kg) (without breech)
Barrel length	40 ft 0 in (12.19 m) bore (40 calibers)
Shell	870 lb (390 kg) armor-piercing
Caliber	12 in (305 mm)
Elevation	Mark 4: −3° to +15° Mark 5: −7° to +20°
Traverse	−150° to +150°
Rate of fire	0.66 rounds per minute (as commissioned) 2 rounds per minute (after 1906)
Muzzle velocity	2,800 ft/s (850 m/s) (as commissioned) 2,600 ft/s (790 m/s) (first derating) 2,400 ft/s (730 m/s) (final derating)
Effective firing range	19,000 yd (17,374 m) at 15.5° elevation

The 12"/40 caliber gun (spoken as "twelve-inch-forty--caliber") were used for the primary batteries of the United States Navy's last class of monitors and the Maine-class and Virginia-class pre-dreadnought battleships.^[1]