The Mark 12 5"/38-caliber gun was a United States dual-purpose naval gun, but also installed in single-purpose mounts on a handful of ships. The 38-caliber barrel was a mid-length compromise between the previous United States standard 5"/51 low-angle gun and 5"/25 anti-aircraft gun. United States naval gun terminology indicates the gun fired a projectile 5 in in diameter, and the barrel was 38 calibers long. The increased barrel length provided greatly improved performance in both anti-aircraft and anti-surface roles compared to the 5"/25 gun. However, except for the barrel length and the use of semi-fixed ammunition, the 5"/38 gun was derived from the 5"/25 gun. Both weapons had power ramming, which enabled rapid fire at high angles against aircraft. The 5"/38 entered service on USS Farragut (DD-348), commissioned in 1934, the first new destroyer design since the last Clemson was built in 1922. The base ring mount, which improved the effective rate of fire, entered service on USS Porter (DD-356), commissioned in 1936. Among naval historians, the 5"/38 gun is considered the best intermediate-caliber, dual purpose naval gun of World War II, especially as it was usually under the control of the advanced Mark 37 Gun Fire Control System which provided accurate and timely firing against surface and air targets. Even this advanced system required nearly 1000 rounds of ammunition expenditure per aircraft kill. However, the planes were normally killed by shell fragments and not direct hits; barrage fire was used, with many guns firing in the air at the same time. This would result in large walls of shell fragments being put up to take out one or several planes or in anticipation of an unseen plane, this being justifiable as one plane was capable of significant destruction. The comparatively high rate of fire for a gun of its caliber earned it an enviable reputation, particularly as an anti-aircraft weapon, in which role it was commonly employed by United States Navy vessels. Base ring mounts with integral hoists had a nominal rate of fire of 15 rounds per minute per barrel; however, with a well-trained crew, 22 rounds per minute per barrel was possible for short periods. On pedestal and other mounts lacking integral hoists, 12 to 15 rounds per minute was the rate of fire. Useful life expectancy was 4600 effective full charges (EFC) per barrel. The 5"/38 cal gun was mounted on a very large number of US Navy ships in 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 3990 lb. The Mark 12 Gun Assembly was introduced in 1934, where it was first used in single pedestal mounts on the Farragut-class destroyers, 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: The new gun initial muzzle velocity is 2600 ft/s, and the gun life average initial muzzle velocity is about 2500 ft/s. US ships during World War II carried only small quantities of special common ammunition, as the anti-aircraft common was considered more useful, even if it meant achieving much less armor penetration. Bursting charges were 7.25 lb explosive D composition A, the special common had only 0.9-1.2 kg due to its thicker walls (AP).

Loading

At the "LOAD" command, or if the mount is executing "RAPID" loading: (NOTE: Rapid loading means that, when the gun fires, the gun crew immediately reloads the gun without command until "CEASE FIRE" or "CHECK FIRE" is given.) The Powder-Man: The Projectile-Man: Rammer Load Cycle:

Firing

This gun can be fired either electrically or by percussion. When the gun fires, the following automatic events happen in two seconds: The gun is ready to be reloaded.

Gun mounts

Types

There are four basic mount types: Farragut and Mahan had only open mounts. The Gridley class introduced the enclosed single gun house, but not all of its guns were enclosed. The Benham class replaced all pedestal mounts with open base ring mounts later on. The Fletcher class was the first to only have enclosed guns (except for the Porter and Somers destroyer leaders). There are several models of the 5"/38, differentiated by the word Mark (or its abbreviation MK) and a number. Variations to the basic design are called Modifications (or its abbreviation Mod). For instance, 5"/38 MK 21 is a single-barrel open pedestal mount widely used on amphibious ships, auxiliaries, and merchant ships. The 5"/38 MK 30 is a single enclosed base ring mount widely used on destroyer escorts. The 5"/38 MK 38 is a twin mount specifically designed for newer destroyers.

Ammunition delivery

Since this gun fires semi-fixed ammunition, each round is delivered to the gun in two pieces—a projectile and a powder case.

Mount crew

Depending on the mount, a 5"/38-caliber gun could have a crew of 15 to 27 personnel in the gun room and upper handling room. This does not include the personnel needed in the magazines during extended actions. There were two modes of mount operation that the crew was trained and expected to know. The primary mode was "automatic control", where the mount was slaved to the fire control system. But if the fire control system was damaged, or if the ship's power was out, the mount could continue the action in "local control". In US service, most gun crews were US Navy personnel. Even the civilian Merchant Marine ships had a small detachment of the Navy Armed Guard on board to operate the 5"/38 and other guns. One exception to this was on ships with a Marine Detachment, where the Marines manned one of the mounts, usually decorated with the Marine emblem (see the USMC emblem on USS New Jersey's Mk 28, Mod 2 mount picture above).

Ammunition

This gun uses semi-fixed ammunition. (Pictured) (Also called Separated Ammunition.) Each round consists of a projectile and a powder case. The two parts of the round are kept separate until they get to the gun. At the gun, they are first combined on the rammer tray, and then power rammed into the chamber together with one ram cycle. The powder case completely fills the volume of the chamber, and its length seats the projectile's rotating band into the bore's rifling. This is different from a naval bag gun. In a bag gun: (1) The projectile, by itself, is power rammed into the chamber until its rotating band is seated in the bore's rifling. (2) The rammer is retracted. (3) The powder bags are then rammed in. This is also different from some artillery field guns: (1) The projectile is hand rammed into the chamber with a ramrod until its rotating band is seated in the bore's rifling. (2) The ramrod is retracted. (3) Next powder is placed in the chamber either as a bag or primed canister with the required charge. Note that the single ram operation used in semi-fixed guns decreases the loading time, and therefore increases the firing rate on medium and large caliber guns. For example, each of the nine 8"(203 mm)/55-caliber Rapid-Fire guns installed on the Des Moines-class cruiser used auto-loaded semi-fixed ammunition and had a firing rate of 10 to 12 rounds a minute. See also the 8"/55 caliber Mark 71 gun. 5” rounds were often used as weights for burials at sea.

Projectile

The Projectile (pictured) has three major parts: the body, the fuze, and the explosive charge. The body is basically a machined steel tube with an ogive shape at one end. At the ogive and rear ends are threaded openings used to the install the shell's filler and hold the fuzes. Around the tube near the base is a copper alloy ring called the Rotating Band. This band has a diameter larger than the bore, and when the projectile and powder case are rammed into the chamber, the band is jammed into the grooves of the bore's rifling. It forms a gas seal between the projectile and the bore. Also, as the projectile travels down the barrel, the band grips the rifling to impart spin to the projectile. The Fuse detonates the projectile to cause maximum damage to the target. Different targets required different fuzes. The safety requirements of a fuze are that... All of these events must take place in the correct order to arm the fuze. List of fuze types:

Powder case

The powder case is a brass or steel alloy cylinder closed at one end. It holds the propelling charge and a case combination primer. The charge is held packed around the primer by a wad, distance piece (not in clearing charge), and plug. When rammed in the chamber with the projectile, the Full and Reduced charge cases are designed to completely fill the volume of the chamber from the breechblock face to the base of the projectile when its rotating band is jammed into the bore's rifling. In other words, the powder case acts a rammer extension for the projectile. There are three types of powder cases:

Deployment

(to be moved to a suitable page) Aircraft carriers Escort Carriers Battleships Heavy cruisers Light cruisers Destroyers Destroyer escorts Attack Transports Attack Cargo

Weapons of comparable role, performance and era

Weapons of comparable role in successive U.S. Navy service