Mounted on both the "North Carolina" class and the follow-up , the nine 16 in/45 were improved versions of the guns mounted on the s, hence the designation of "Mark 6". A major alteration from the older guns was the Mark 6's ability to fire a new armor-piercing (AP) shell developed by the Bureau of Ordnance. At full charge with a brand-new gun, the heavy shell would be expelled at a muzzle velocity of . At a reduced charge, the same shell would be fired at . Barrel life—the approximate number of rounds a gun could fire before needing to be relined or replaced—was 395 shells when using AP, although if only practice shells were used this figure was significantly higher: 2,860. Turning at 4 degrees a second, each turret could to 150 degrees on either side of the ship. The guns could be elevated to a maximum inclination of 45 degrees; turrets one and three could depress to −2 degrees, but due to its superfiring position, the guns on turret two could only depress to 0 degrees.