5-inch/38-caliber gun

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-calibers long barrel was a mid-length compromise between the previous United States standard 5-inch/51 low-angle gun and 5-inch/25 anti-aircraft gun. The increased barrel length provided greatly improved performance in both anti-aircraft and anti-surface roles compared to the 5-inch/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, 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, 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 1,000 rounds of ammunition expenditure per aircraft kill. However, the planes were normally brought down 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 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 Mk 12 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
;Hand loaded
;Power rammed
;Vertical sliding-wedge breech block
;Hydraulic recoil
;Pneumatic counter-recoil
;Barrel designation :5" is the caliber of this gun. The term "caliber" used here is the artillery caliber definition, and its value is equal to the bore diameter as measured from land to land. Lands are the raised portions of the bore rifling, between the grooves..38 caliber means that the barrel from breech face to muzzle is 38 calibers in length. As this gun's caliber is 5 inches, its barrel length is 38 times 5 inches:.
;Barrel description :

Radially expanded monobloc steel alloy.
Weight:
The bore is chrome plated from the origin of rifling to the muzzle.
45 groove rifling with a full uniform right hand twist in 30 Calibers.
Maximum bore pressure of a new gun firing an anti-aircraft common projectile:.
Barrel connected to the housing with a bayonet joint that allowed for its replacement by destroyer tenders in the theater of operation, without dismantling the breech mechanism or other parts.

;Ballistics: Maximum horizontal range with a projectile is. In the anti-aircraft role, the gun has a ceiling of at 85 degrees elevation.
;Armor penetration with special common shell:
;Range with AAC Mark 49 :
The new gun initial muzzle velocity is, and the gun life average initial muzzle velocity is about.
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 explosive D composition A, the special common had only 0.9-1.2 kg due to its thicker walls.

Loading

At the "LOAD" command, or if the mount is executing "RAPID" loading:
The Powder-Man:

Verifies that the RAMMER SPADE is at the rear of the "Rammer Tray"
Slips the "Butterfly" primer protector off the base of the powder case that is sticking knee high out of powder hoist on the deck.
Throws the protector out of the mount.
Pulls the powder case out of the hoist, and lifts it into the rammer tray.
Verifies that the case is back against the rammer spade.
Clears his arms from the tray.

The Projectile-Man:

Verifies that the powder case is in the rammer tray.
Pulls the projectile out of the waist high projectile hoist.
Places projectile in front of the powder case in the tray.
Clears his arms from the tray.
Pulls down on the RAMMER CONTROL.

Rammer Load Cycle:

Pulling down on the Rammer Control lever opens hydraulic valves inside the Rammer Controller.
The opened valves port high pressure hydraulic fluid to the "Hydraulic Ram Cylinder" in the Slide behind the tray. The Ram Cylinder is connected to the "Rammer Cross Head". The Cross Head supports the Rammer Spade as it moves in the tray. When the cylinder is pressurized, the Cross Head and Spade are driven forward in the Tray.
As the spade moves forward, it pushes the projectile and powder case into the chamber. The spade's time of travel, from the rear of the tray to the breech, is one second. As it approaches the breech, the Cross Head pushes through a spring latch that locks it there. At the same time, the Cross Head trips another lever connected to the Rammer Controller, and the Controller releases the hydraulic pressure to the Ram Cylinder.
When the powder case clears the top of the breech block, the block automatically rises.
The rising breech block displaces the rammer spade behind the powder case by pushing the spring-loaded spade up. This continues until the rammer spade is off the powder case, and the block has sealed the chamber.
The gun is loaded and ready to fire.

Firing

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

During Recoil:
# The Rammer Crosshead is unlocked.
# The Rammer Control is pushed to the up position by a cam on top of the rearward moving Housing.
# With the Rammer Control up, the Rammer Controller ports high pressure hydraulic fluid to the retract side of the Rammer Cylinder, and the Rammer Crosshead and Spade drive back to the rear of the Rammer Tray.
During Counter-recoil:
# The Firing Pin is cocked.
# The Breech Block is lowered.
# The spent Powder Case is ejected out of the Chamber, and back down the Rammer Tray. There it is caught by the gloved Hot Case Man, and thrown out of the mount.
# Just before the housing finishes returning to "In Battery", a valve is opened for a second, and a blast of compressed air is sent down the bore to clean it out.

The gun is ready to be reloaded.

Gun mounts

Types

There are four basic mount types:
;Twin :

All sat on a base ring stand, and had an ammunition handling room, called the Upper Handling Room, below the mount.
They all had:
* Horizontal periscopic sights with movable-prism sight setting.
* Two powered, fuze setting, projectile hoists.
* Two powered powder case hoists.
* Powered training and elevating drives.
This mount was the standard installation on battleships, cruisers, early destroyer leader classes, and later destroyers. It was also used on the island side of the s.

;Enclosed single:
;Open single base ring mount:
;Open single pedestal mount:
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.
There are several models of the 5"/38, differentiated by the word Mark and a number. Variations to the basic design are called Modifications. 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.

Mark/mod	Barrels	Weight	Design	Use
Mk 21	Single		Open pedestal	Some 1930s built combatants, auxiliaries, merchant ships destroyers * 8 * 16
Mk 22	Twin		Enclosed base ring	destroyer leaders * 8 * 5
Mk 24	Single		Open pedestal	1930s built aircraft carriers destroyers * 4 * 8 * 2 cruisers *
Mk 28 MOD 0	Twin		Enclosed base ring	Pre-Iowa-class battleships
Mk 28 MOD 2	Twin		Enclosed base ring	Iowa-class battleships
Mk 29 MOD 0	Twin		Enclosed base ring	Cruisers, Atlanta-class light cruisers
Mk 30 MOD 0	Single		Enclosed base ring	Destroyers, auxiliaries, USCG high endurance cutters cruisers *
Mk 30 MOD 1	Single		Open base ring	Destroyer rear mounts, escort carriers 10 12 30 66
Mk 30 MOD 69	Single		Enclosed base ring	Destroyer escorts with the upper rear edge of the Mark 38 blast shield beveled to clear hedgehog projectiles from a launcher astern of the gun mount
Mk 32 MOD 0	Twin		Enclosed base ring	Cruisers, aircraft carriers
Mk 32 MOD 4	Twin		Enclosed base ring	Cruisers, aircraft carriers
Mk 37 MOD 0	Single		Open pedestal	Armed merchants, auxiliaries
Mk 38 MOD 0	Twin		Enclosed base ring	Destroyers

Ammunition delivery

Since this gun fires semi-fixed ammunition, each round is delivered to the gun in two piecesa projectile and a powder case.
;Base ring mounts
;Pedestal mounts

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.
;Mount captain
;Gun Captain
;Pointer
;Trainer
;Sight setter
;Fuze setter
;Powder-man
;Projectile-man
;Hot case man
;Check sight

Ammunition

This gun uses semi-fixed 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: The projectile, by itself, is power rammed into the chamber until its rotating band is seated in the bore's rifling. The rammer is retracted. The powder bags are then rammed in. This is also different from some artillery field guns: The projectile is hand rammed into the chamber with a ramrod until its rotating band is seated in the bore's rifling. The ramrod is retracted. 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"/55-caliber Rapid-Fire guns installed on the 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 has three major parts: the body, the fuze, and the explosive charge.
;Projectile body
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.
;Fuze
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...

... it is safe to handle.
... it remains unarmed in the bore, and until the projectile is well clear of the firing ship to protect exposed personnel. Therefore, when the gun is fired, the following events take place:
* 14,000g acceleration from the burning propellant in the bore. This acceleration is used to setback some fuze parts from unarmed to armed positions due to their inertia.
* Centrifugal force from the 12,360 rpm projectile rotation. This force causes other parts to move outward.
* 7.2g deceleration from aerodynamic drag after the projectile leaves the muzzle. Due to inertia, other movable parts will creep forward.

All of these events must take place in the correct order to arm the fuze.
List of fuze types:
;Mechanical time fuze
;Base detonating fuze
;Point detonating fuze
;VT fuze
;Auxiliary detonating fuze

Body label	Full name	Description
AA	Anti-aircraft	A high capacity fragmenting shell with a nose mechanical time fuze
AAC	Anti-aircraft common	A medium penetrating shell with a mechanical time fuze and a base detonating fuze. Designed to be used on either aircraft or lightly armored ships. For aircraft, the time fuze is set to explode the shell just before it reaches the target. The detonation shock wave and the expanding cone of shrapnel increases the chance of target destruction. For vessels, the time fuze is left on safe, and the base detonating fuze will explode the shell 25 milliseconds after impact.
AAVT	Anti-aircraft VT	A high capacity fragmenting shell with a VT fuze.
AP	Armor-piercing	A thick walled penetrating projectile with a base detonating fuze. The explosive charge is usually Explosive D because it is less sensitive to impact.
SS	Star shell	A thin walled shell with a mechanical time fuze. Packed inside is a flare attached to a parachute. When the fuze fires, a small black powder charge expels the flare and parachute out the back. Before radar, star shells were used to illuminate the target at night. They are still used in support of troops at night, or illumination of an at sea rescue.
WP	White phosphorus	A thin walled shell with a point detonating fuze used for smoke screens. It also has some incendiary effect.
AA non-frag	Anti-Aircraft non-fragmentation	A thin walled shell with a mechanical time fuze and packed with a smoke producing chemical that is ejected out the rear by a small black powder charge. It is used in practice anti-aircraft shoots.
AAVT non-frag	Anti-Aircraft VT non-fragmentation	A thin walled shell with a VT fuze and packed with a smoke producing chemical that is ejected out the rear by a small black powder charge. It is used in practice anti-aircraft shoots.
BL	Blind load	A shell without a fuze, and filled with sand. It is used in practice surface shoots.
W	Window	A thin walled shell with a mechanical time fuze and packed with strips of metal foil that is ejected out the rear by a small black powder charge. It is used to confuse enemy radar.

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, 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

Aircraft carriers

3 8
8
24 12

Escort Carriers

50 1
19 2

Battleships

2 20
3 of 4 20
16
4 20

Heavy cruisers

12
12
8
14 12
3 12
3 12

Light cruisers

2 8
4 16
4 Atlanta 12
27 12
2 12
3 12

Destroyers

8 5
8 8
18 5
4 4
8 4
5 8
10 4
12 5
6 5
24 repeat-Bensons 4
18 5
48 repeat-Gleaves 4
175 5
58 6
12 6
98 6

Destroyer escorts

22 2
50 Rudderow-APDs 1
83 2
6 1

Attack Transports

7 of 328 Type C2 ship
* 3 2
* 4 2

Attack Cargo

74 of 328 Type C2 ship
* 1
* 11 1
* 32 1
* 30 1

Weapons of comparable role, performance and era

QF 4.7 inch Mark XI gun : British equivalent dual-purpose gun.
QF 4.5 inch Mk I – V naval gun : British equivalent dual-purpose gun.
12.7 cm SK C/34 naval gun : German equivalent limited to low-angle fire.
12.8 cm FlaK 40 : Dedicated anti-aircraft, land-based German gun of equal calibre.
130 mm/50 B13 Pattern 1936 : Soviet equivalent naval and coastal gun.
Canon de 138 mm Modèle 1929 : French equivalent naval gun.
120 mm naval gun : Italian equivalent naval gun.
12.7 cm/50 Type 3 naval gun : Japanese equivalent naval gun mounted on most destroyers and competitive against surface targets
10 cm/65 Type 98 naval gun: Japanese naval gun mounted on destroyers, aircraft carrier and light cruiser, competitive in the anti-aircraft role