5 " / 38 caliber gun The Mark 12 5 " / 38 caliber gun was a US naval gun . The gun was installed into Single Purpose and Dual Purpose mounts used primarily by the US Navy . On these 5 " mounts , Single Purpose ( SP ) means that the mount is limited to 35° elevation with no provision for AA shell fuze setters , and is designed to fire at surface targets only , while Dual Purpose ( DP ) means that it is designed to be effective against both surface and aircraft targets because it can elevate to 85° and has on mount AA shell fuze setters . 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 in diameter , and the barrel was 38 calibers long , making the 5 " / 38 dual purpose midway in barrel length between the 5 " / 51 surface - to - surface and the 5 " / 25 anti - aircraft guns . 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 base ring mount , which improved the effective rate of fire , entered service on USS Gridley ( DD - 380 ) , commissioned in 1937 . Among naval historians , the 5 " / 38 gun is considered the best intermediate - caliber , dual purpose naval gun of World War II , especially when it was usually under the control of the advanced Mark 37 Gun Fire Control System which provided accurate and timely firing solutions 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 calibre 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 charge s ( 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 One - 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 . < ref name = " 5 / 38 " > < / ref > 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 : US ships during World War II carried only small quantities of Special Common ammunition as the AA Common were considered more useful as all around multirole ammunitions , even if this meant much less armour penetration . Bursting charges were 7 . 25 lbs . ( 3 . 3 kg ) Explosive D Composition A , the Special Common had only 0 , 9 - 1 , 2 kg due to its thicker walls ( AP ) . Loading and firing . At the " load " command , the powder - man slips a primer protector off the end of the powder case , extracts the case from the scuttle or rack , and lifts it into the gun ' s rammer tray . Meanwhile , the projectile - man pulls a projectile out of the hoist or fuze setter , places it in the rammer tray in front of the powder case , and then pulls down on the rammer lever . This causes the power rammer to ram the projectile and powder case into the chamber . As the powder case clears the top of the breech block , the block automatically rises to seal the chamber . The gun is ready to fire . The case combination primer in the base of the powder case can be fired either electrically or by percussion . When the gun fires , the recoil ’ s rearward motion returns the rammer lever to the up position , and the rammer drives back to the rear of the rammer tray . During counter - recoil , the breech block is automatically lowered and the spent powder case is ejected from the chamber . When the gun has returned to battery , 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 : 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 escort s . 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 from 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 the 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 form 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 " ( 203mm ) / 55caliber 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 . 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 fuze detonates the projectile to cause maximum damage to the target . Different targets required different fuzes . The most important requirement of a fuze is that it remains unarmed until the projectile is well clear of the gun ' s muzzle on the firing ship . To do this , the fuze remains unarmed until a series of events take place . The first event is the shock of firing . The 5 " / 38 cal projectile experiences at least a 14 , 000 g acceleration as it is pushed down the barrel by the burning propellant . This acceleration causes parts of the fuze to setback due to their inertia , and they shear pins that hold them in the unarmed position . The second event is the spinning of the projectile due to the bore ' s rifling . The 5 " / 38 cal projectile spins at more than 200 revolutions per second when traveling at per second ( New gun initial velocity ) . The centrifugal force of this spin causes other parts to move outward . The third event is the projectile ' s deceleration after it leaves the muzzle , and other parts creep forward . 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 :