page_title: Armament of the Iowa-class battleship
section_title: Mark 12 gun assembly
hierarchical_section_title: Armament of the Iowa-class battleship / Secondary battery / Mark 28, Mod 2 mounts / Mark 12 gun assembly
caption_attribution_description: Mk 12 5in/38cal gun assembly. Cropped portion of image scanned from source.
context_page_description: The Iowa-class battleships were the most heavily armed gunships the United States Navy has ever put to sea due to the continual development of their onboard weaponry. The first Iowa-class ship was laid down in June 1940; in their World War II configuration, each of the Iowa-class battleships had a main battery of 16-inch guns that could hit targets nearly 20 statute miles away with a variety of artillery shells designed for anti-ship or bombardment work. The secondary battery of 5-inch guns could hit targets nearly 9 statute miles away with solid projectiles or proximity fuzed shells, and were effective in an anti-aircraft role as well. Each of the four battleships carried a wide array of 20 mm and 40 mm anti-aircraft guns for defense against enemy aircraft.
  When reactivated and modernized in the 1980s each battleship retained the original battery of nine 16-inch guns, but the secondary battery on each battleship was reduced from ten twin-gun mounts and twenty guns to six twin-gun mounts with 12 guns to allow for the installation of two platforms for the Tomahawk missiles.
context_section_description: The Mk 12 Gun Assembly (pictured) was a semi-automatic, power rammed, vertical sliding-wedge breech block type gun. The Gun Assembly shown in the picture is the mount's right gun. The left gun is the mirror image of the right gun. Since this gun assembly fired semi-fixed ammunition, (pictured) each round was delivered to the guns in two pieces. Each gun, in this twin mount, had its own projectile hoist and powder case hoist from the upper handling room. The electric-hydraulic projectile hoist would deliver a projectile next to the projectile man with the nose down and waist high. The electric-hydraulic powder case hoist poked the case through a powder scuttle in the gun room's deck just next to the powder man's feet.  At the load command, the powder man would slip a primer protector off the end of the powder case, extract the case from the scuttle, and lift it into the gun's rammer tray.
  Meanwhile, the projectile man would pull a projectile out of the hoist, and place it in the rammer tray in front of the powder case. Then, as he turned to get the next projectile out of the hoist, the projectile man would pull down on the rammer lever. This caused the power rammer to ram the projectile and powder case into the chamber. As the powder case cleared the top of the breechblock, the block would rise to seal the chamber. The gun was ready to fire. The case combination primer in the base of the powder case could be fired either electrically or by percussion. Electrical firing was the preferred method because the firing circuit could be energized by firing keys down in the plotting room when firing salvos at surface targets, or up in the director when firing at air targets. Percussion firing could be executed by the Pointer (man controlling elevation) by pushing a foot treadle. When the gun fired, the recoil's rearward motion returned the rammer lever to the up position, and the rammer would drive back to the rear of the rammer tray. During counter-recoil, the breechblock was automatically lowered and the spent powder case was ejected from the chamber. When the gun returned to battery, a blast of compressed air was sent down the bore to clean it out. The gun was ready to be reloaded.
caption: Mk 12 Gun Assembly (right gun)
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