12-inch/40-caliber gun
# 12-inch/40-caliber gun

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.

## Design

The 12-inch (305 mm)/40 caliber gun was developed after the Spanish–American War to use the new smokeless powder that had recently been adopted by the Navy. The Mark 3, gun Nos. 15–48 and 50–56, was constructed of tube, jacket, and eight hoops. It was found that the early guns suffered from excessive bore erosion, in an attempt to fix this the Navy reduced the propellant charges to reduce the muzzle velocity, because of this the Mark 4, gun Nos. 49, 58–60, 150–154, and 179, was similar to the Mark 3 but with a smaller chamber for the reduced propellant charge.

## Service history

The guns mounted in the Virginia-class battleships were in an unusual two-level turret with the 8-inch (203 mm)/45 caliber guns on top of the larger 12-inch guns. This arrangement ultimately proved unsuccessful but helped the Navy in the successful development of superfiring turrets later used in the dreadnought South Carolina.

## Incident

Gun No. 49, while testing powder at the Naval Proving Ground, had the entire muzzle and chase blow off. The board appointed to investigate came to the conclusion that the new powder, while performing properly, caused a pressure along the chase that was dangerously close to the strength curve. It was decided that when the guns were withdrawn to be relined they would add an additional hoop that extended to the muzzle would be placed on the chase.

## Naval Service

| Ship | Gun Installed | Gun Mount |
| - | - | - |
| USS Arkansas (BM-7) | Mark 3 or 4: 12"/40 caliber | Mark 4: 1 × twin turrets |
| USS Nevada (BM-8) | Mark 3 or 4: 12"/40 caliber | Mark 4: 1 × twin turrets |
| USS Florida (BM-9) | Mark 3 or 4: 12"/40 caliber | Mark 4: 1 × twin turrets |
| USS Wyoming (BM-10) | Mark 3 or 4: 12"/40 caliber | Mark 4: 1 × twin turrets |
| USS Maine (BB-10) | Mark 3 or 4: 12"/40 caliber | Mark 4: 2 × twin turrets |
| USS Missouri (BB-11) | Mark 3 or 4: 12"/40 caliber | Mark 4: 2 × twin turrets |
| USS Ohio (BB-12) | Mark 3 or 4: 12"/40 caliber | Mark 4: 2 × twin turrets |
| USS Virginia (BB-13) | Mark 3 or 4: 12"/40 caliber | Mark 5: 2 × dual-caliber turrets |
| USS Nebraska (BB-14) | Mark 3 or 4: 12"/40 caliber | Mark 5: 2 × dual-caliber turrets |
| USS Georgia (BB-15) | Mark 3 or 4: 12"/40 caliber | Mark 5: 2 × dual-caliber turrets |
| USS New Jersey (BB-16) | Mark 3 or 4: 12"/40 caliber | Mark 5: 2 × dual-caliber turrets |
| USS Rhode Island (BB-17) | Mark 3 or 4: 12"/40 caliber | Mark 5: 2 × dual-caliber turrets |
