5"/38 Mk 12 Gun
Page last updated: 24 September, 2016


5"/38 Mark 12

The 5 inch 38-caliber dual-purpose gun has been one of the US Navy's most trusted dual-purpose (that is, used against both air and surface target) weapons since 1935. During WWII approximately 10 different single and twin mountings were developed for 5 inch 38-caliber barrels. In ballistic terms, there is nothing particularly outstanding about the 5 inch 38 (such as projectile weight or Muzzle Velocity), however the general reliability, handling and accuracy were rated as excellent. The 5 inch 38 proved so practical and so effective that it was used not only on destroyers but also on cruisers, battleships and aircraft carriers. However, although the 5 inch 38 was the first used by the US Navy only a few of these guns remain in service today in the US Navy. It is still widely used by many other navies.

The ammunition used in the 5 inch 38 dual-purpose gun was semi-fixed. All rounds used a forged-steel projectile with a single wide copper drive band. Nose fuses were protected by a domed cover until just before loading. The projectile weight for all types is about 55 lbs.

This was unquestionably the finest Dual Purpose gun of World War II.  Originally designed to arm new destroyers being built in the 1930s, the 5"/38 (12.7 cm) wound up being used on nearly every major US warship built between 1934 and 1945 and was still being used on new construction as late as the 1960s.  It was also used on many auxiliaries and smaller warships as well as on US Coast Guard vessels.  This standardization, unique in any navy, greatly helped the logistical supply situation of the Pacific War.

These guns were hand-loaded, but power-rammed, which gave them a high rate of fire and a capability of being easily loaded at any angle of elevation, both of which are highly desirable qualities for an anti-aircraft weapon.  The introduction of proximity-fuzed AA shells in 1943 made this weapon an even more potent AAA gun.

The earliest mountings as used on USS Farragut (DD-348) were pedestal mounts with shell and cartridge hoists located on the deck behind the gun mount.  However, starting with USS Gridley (DD-380), a new base-ring mounting with integral shell hoists on the axis of the mount was introduced.  This type of mounting meant that shells and cartridges could be passed directly to the gun's breech at any angle of train, thus significantly improving the practical rate of fire.  Most subsequent designs, including all twin mountings, were similar, although a simpler base ring mount lacking hoists was introduced in 1943 for use on auxiliary vessels.

There were some teething troubles when this gun was introduced in 1934, but a BuOrd report of 1945 states that during World War II they were considered to be highly reliable, robust and accurate, a reputation they retained even after the end of the war when the 5"/54 (12.7 cm) series of weapons were introduced.  When coupled with the Mark 37 Fire Control System, used on most US warships built between 1939 and 1946, these guns were quite effective in the AA role.  For example, during gunnery trials in 1941, USS North Carolina (BB-55) was able to repeatedly shoot down drone aircraft at altitudes of 12,000 to 13,000 feet (3,700 to 4,000 m), about double the range of the 5"/25 (12.7 cm) AA Mark 10 used on older ships.

These guns were introduced to the British Royal Navy in 1941-1942 when HMS Delhi was rebuilt in New York Navy Yard.  The British were impressed with the combination of the 5" (12.7 cm) gun and Mark 37 Fire Control System and tried to purchase additional units, but the rapid ramping up of US warship construction prevented any diversion.

At least twelve guns were sold to Brazil around 1940 for arming the Marcilio Dias class destroyers.

The Mark A prototype for this gun was created from a cut-down 5"/51 (12.7 cm) Mark 9, the only version of that weapon that used semi-fixed ammunition.

Mods 0 and 1 were of autofretted monobloc construction and used a semi-automatic vertical sliding wedge breech mechanism.  The gun barrel was secured to the housing by a bayonet joint, thus allowing easy barrel replacement.  Mod 2 used a non-expanded barrel of higher strength steel.  Over 8,000 of these weapons were produced between 1934 and 1945, broken down as 2,168 guns in single mountings, 2,714 guns in twin mountings and 3,298 guns in single mountings for auxiliary ships.  These figures may not include guns produced prior to 1 July 1940, at which time there were 315 single, 52 twin SP and eight twin DP mountings in the entire US Fleet.  Average cost was $100,000 per gun assembly, which does not include the cost of the mounting.  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.

The following is extracted from:


B. Five-Inch 38-Caliber Assemblies

8B1. General

The 5”/38 caliber gun is a semiautomatic, dual-purpose, pedestal- or base-ring-mounted gun which uses semifixed ammunition. The principal features of 5”/38 caliber gun assemblies are as follows:

     1. Vertical sliding-wedge breech mechanism.
     2. Hydraulic recoil and hydropneumatic counter-recoil systems.
     3. Power-operated rammer.
     4. Power-operated elevating and training gear.
     5. Movable-prism telescopes.
     6. Power-operated fuze-setting projectile hoist (except on mounts of type 4 listed in article 8B27).
     7. Power-operated powder hoist on all twin mounts and some singles.

The operating principle of the 5”/38 caliber gun is the same for all of the installations found on naval vessels. Minor variations in mechanical features reflect either improvement in design or the special requirements of certain installations. The majority of these variations are in mount design.

The gun, slide, and housing assemblies, the breech mechanism, and their associated parts are almost identical in all mounts. The greatest variation in these parts occurs in the twin mount, in which the gun emplacements form left and right gun assemblies, alike in all respects except for the reversed left and right arrangements of the two gun, slide, and housing assemblies, the breech mechanism, and their component parts. Each assembly is mounted separately in carriages on a large rectangular platform. This difference changes the appearance of the gun assembly but does not affect the mechanical operating principles.

Twin mount assemblies are installed on battleships, cruisers, carriers, and destroyers. Single mounts are found on carriers and destroyer escorts and on many of the older cruisers and destroyers, as well as on various types of mine-craft, landing craft, patrol craft, and auxiliaries.

The main purpose of this section is to describe the basic features, the function, and the mechanical operation of the 5”/38 caliber twin mount assembly. In as much as the two gun assemblies are identical in operating principles, only the right assembly will be discussed, unless otherwise stated. Other types of 5”/38 mounts are discussed briefly at the end of the section.

8B2. Ammunition

The gun uses semifixed ammunition consisting of a 54-pound projectile and a case assembly weighing about 28 pounds, which includes a 15-pound powder charge. The projectiles used are antiaircraft common, common, illuminating, and WP smoke. The ballistic performance obtained with a 15-pound service charge is as follows: initial velocity, 2,600 feet per second; maximum horizontal range, 18,000 yards; maximum vertical range, 37,300 feet. The gun is capable of sustained firing at a rate well in excess of any which can be attained by the loading crew. An experienced crew can load about 15 rounds per minute for long periods, and may attain a short-period rate of 22 rounds per minute.

8B3. Gun

The gun is a radially expanded monobloc barrel which weighs about 2 tons. The rifling has a uniform twist of 1 turn in 30 calibers. The bore is chromium-plated from the forward portion of the powder chamber to the muzzle. The barrel is connected to the housing by means of a bayonet-type joint and locked by a key and key-bolt seated in a keyway in the barrel. This design facilitates regunning the mount without dismantling the breech mechanism or other parts.



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