the World War II era. It was backfitted to many of the World War I-era battleships during their wartime refits, usually replacing 5"/25 guns that were fitted in the 1930s. It has left active US Navy service, but it is still on mothballed ships of the United States Navy reserve fleets. It is also used by a number of nations who bought or were given US Navy surplus ships. Millions of rounds of ammunition were produced for these guns, with over 720,000 rounds still remaining in Navy storage depots in the mid-1980s because of the large number of Reserve Fleet ships with 5"/38 cal guns on board. Mark 12 5"/38 cal gun assembly Each mount carries one or two Mk 12 5"/38cal Gun Assemblies. The gun assembly shown is used in single mounts, and it is the right gun in twin mounts. It is loaded from the left side. The left gun in twin mounts is the mirror image of the right gun, and it is loaded from the right side. The Mk12 gun assembly weighs . The Mark 12 Gun Assembly was introduced in 1934, where it was first used in single pedestal mounts on the s, but by the time of World War II they had been installed in single and twin mounts on nearly every major warship and auxiliary in the US fleet. Characteristics The major Mk12 Gun Assembly characteristics are: Semi-automatic During recoil, some of the recoil energy is stored in the counter-recoil system. That stored energy is used during counter-recoil to prepare the gun for the next round. The firing pin is cocked, the breech is opened, the spent propellant case is ejected, and the bore is cleared of debris with an air blast. Hand loaded A projectile-man and a powder-man are stationed at each gun assembly. Their job is to move the round, consisting of a projectile and a propellant case, from the hoists to the rammer tray projecting from the gun's breech, and then start the ram cycle. The powder case is placed first and the projectile rests against the powder case. Power rammed This gun used a electric-hydraulic power rammer that was designed to ram a , round (combined weight of projectile and propellant) into the chamber at any gun elevation in less than one second. The rammer's control box, hydraulic fluid tank and AC motor are bolted to the top of