United States of America
5"/38 (12.7 cm) Mark 12
Updated 24 February 2013

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, merchant vessels 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 the ammunition supply points located in the fixed structure behind the gun mounts.  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 also 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 and rearmed at the 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.  However, these guns were provided as part of the armament of the escort carriers and repair ships built in the USA for British use.  In 1944, the British proposed that the Nelson class battleships replace their 6" (15.2 cm) and 4.7" (12 cm) mixed purpose batteries with six twin 5"/38 (12.7 cm) DP mountings, but this never proceeded past the planning stage.

At least twelve guns were sold to Brazil around 1940 for arming the Marcilio Dias class destroyers.  At least 24 additional guns were sold to Brazil post-war for arming the Acre 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.


USS Atlanta CL-51 refueling in October 1942
Early units of the Atlanta Class light cruisers carried sixteen 5"/38 (12.7 cm) guns of which fourteen could fire abeam, giving them the heaviest AAA broadside of any USN warship of World War II
U.S. Naval Historical Center Photograph # NH 97807

Click here for additional pictures
Gun Characteristics
Designation 5"/38 (12.7 cm) Mark 12
Ship Class Used On 1934 to 1948

First used on USS Farragut (DD-348)

Used on nearly all World War II-era new-construction warships destroyer-sized and larger along with many auxiliaries, merchant vessels and small warships

Also used to rearm older ships such as battleships and USS Saratoga (CV-3)

Britain:  HMS Delhi as rearmed, Ameer class escort carriers, Assistance class repair ships

Brazil:  Marcilio Dias class and Acre class destroyers

Post-World War II

USA:  Brooke (FFG-1), Garcia (FF-1040), Long Beach (CGN-9), Albany (CG-10) and USCG Hamilton (WHEC-715) classes

Danish:  Peder Skram class frigates

Italian:  Impetuoso (D558) and San Giorgio (D562) classes

Date Of Design about 1932
Date In Service 1934
Gun Weight 3,990 lbs. (1,810 kg) without breech
Gun Length oa 223.8 in (5.683 m)
Bore Length 190 in (4.826 m)
Rifling Length 157.2 in (3.994 m)
Grooves 45
Lands N/A
Twist Uniform RH 1 in 30
Chamber Volume 654 in3 (10.72 dm3)
Rate Of Fire Pedestal and other mounts lacking integral hoists:  12 - 15 rounds per minute

Base ring mounts with integral hoists:  15 - 22 rounds per minute


1) Barrel was chrome plated from the muzzle to include all rifling, the projectile band slope and the forward portion of the chamber.  Total length of plating was 164.5 in (4.178 m) and was 0.00050 in (0.0127 mm) thick.

2) The guns installed on HMS Delhi had originally been destined for USS Edison (DD-439).  These guns had been hand-picked by Edison's first commanding officer, Lt. Cmdr. Albert C. Murdaugh, who had just previously been assigned to the Naval Gun Factory at Washington, D.C.  Much to Lt. Cmdr. Murdaugh's distress, President Roosevelt ordered these guns diverted to Delhi and as a result Edison did not receive her replacement guns until after she had been commissioned and had completed her preliminary trials.  Perhaps as a result of having these hand-picked weapons, the gunnery officer on Delhi reported that during gunnery trials in February and March 1942 that these guns were able to fire 25 rounds per minute with the ready-use ammunition stored in the handling rooms and 15 rounds per minute with the normal supply from the magazines.

3) Projectile travel was 161.34 inches (4.098 m).

Type Separate
Projectile Types and Weights
(see Note 1)
AAC Mark 34 Mod 10 - 55.18 lbs. (25.0 kg)
AAC Mark 35 Mods 1 to 12 - 55.18 lbs. (25.0 kg)
AAC Mark 47 Mods 0 and 1 - 55.18 lbs. (25.0 kg)
AAC Mark 49 - 55.18 lbs. (25.0 kg)
AAC Mark 52 - 55.18 lbs. (25.0 kg)
AAC Mark 56 - 55.18 lbs. (25.0 kg)
Common Mark 32 Mods 1 to 4 - 54.0 lbs. (24.5 kg)
AAVT Mark 31 Mods 1 to 11 - 55.12 lbs. (25.0 kg)
Special Common Mark 38 Mods 1, 2 and 3 - 55.18 lbs. (25.0 kg)
Special Common Mark 46 Mods 1 and 2 - 55.18 lbs. (25.0 kg)
RAP Mark 57 - 54.3 lbs. (24.6 kg)
Illum Marks 27, 30, 44 and 45 - 54.39 lbs. (24.7 kg)
WP Mark 46 - 53.00 lbs. (24.0 kg)
Chaff Mark 78 - 55.3 lbs. (25.1 kg)
Bursting Charge AAC Mark 34 - 7.25 lbs. (3.3 kg) Explosive D Composition A
AAC Mark 35 - 7.25 lbs. (3.3 kg) Explosive D Composition A
AAC Mark 47 - 7.11 lbs. (2.8 kg) Explosive D Composition A
AAC Mark 52 - 7.5 lbs (3.4 kg) Explosive D Composition A
AAC Mark 52 - 8.4 lbs. (3.8) kg RDX/Wax 91/9 Composition A-3
AAC Mark 56 - 7.5 lbs. (3.4 kg) Explosive D Composition A
AAVT Mark 31 - 7.25 lbs. (3.3 kg) Explosive D Composition A
Special Common Mark 38 - 2.04 lbs. (0.9 kg) Explosive D
Common Mark 32 - 2.58 lbs. (1.2 kg) Explosive D
RAP - 3.5 lbs. (1.6 kg) Explosive D
Projectile Length AAC - 20.75 in (52.7 cm)
Common - 20.75 in (52.7 cm)
AAVT - 20.75 in (52.7 cm)
Special Common - 20.75 in (52.7 cm)
Illum - 20.0 in (50.8 cm)
WP - 20.0 in (50.8 cm)
Cartridge Case Type, Size and Empty Weight
(see Note 11)
Marks 5, 8 and 10 - Brass, 127 x 679 mm, 12.31 lbs. (5.58 kg)
Mark 5 Modified - Brass, 127 x 413 mm), N/A
Propellant Charge
(see Note 12)
Full Charge - 15.2 to 15.5 lbs. (6.9 to 7.03 kg) SPD or SPDN D272
Full Charge - 17.2 lbs. (7.8 kg) Universal D264
Full Flashless Charge - 16.0 lbs. (7.3 kg) SPDF D274

Reduced Charge - 3.6 lbs. (1.6 kg) SPDN D282

Muzzle Velocity Full Charge - New gun:  2,600 fps (792 mps)
Full Charge - Average gun:  2,500 fps (762 mps) 

Reduced Charge - New gun:  1,200 fps (366 mps)

Working Pressure 18.0 tons/in2 (2,835 kg/cm2)
Approximate Barrel Life 4,600 rounds
Ammunition stowage per gun
(see Notes 2 and 3)
Yorktown (CV-6) and Essex (CV-9):  450 rounds

North Carolina (BB-55), South Dakota (BB-57) and Iowa (BB-61):  450 rounds

Alaska (CB-1):  500 rounds

Baltimore (CA-68), Oregon City (CA-122) and Des Moines (CA-134):  500 rounds

Saint Louis (CL-49), Cleveland (CL-55) and Fargo (CL-106):  500 rounds

Atlanta (CL-51):  450 rounds

Pre-war destroyers of the Farragut (DD-348) through Sims (DD-409) classes:  300 rounds

Benson (DD-421) and Gleaves (DD-423):  320 - 360 rounds

Fletcher (DD-445):  350 rounds (420 in later ships)

Allen M. Sumner (DD-692) and Gearing (DD-710):  360 rounds

Others:  N/A


1) Special Common had a windscreen with a thin hood and the body was strengthened to enhance its armor piercing qualities.  Postwar, some Special Common were given a dye bag for spotting.  Available colors were blue, green, orange and red.  Common Mark 32 had a windshield but no cap.  AAC Mark 35 and Mark 49 projectile bodies could be used with Point Detonating (PD), Mechanical Time (MT) or with proximity (VT) nose fuzes.  When issued with MT or VT fuzes they were considered as being AA rounds, but when issued with PD fuzes, they were considered to be HC rounds.  Changing the fuze also resulted in slight changes in the total projectile weight and burster weight.  For example, the Mark 35 with PD fuze weighed 54.3 lbs. (24.63 kg) total with a 7.55 lbs. (3.42 kg) burster.  Controlled Variable Time (CVT) fuzes were introduced post-war.  AAC Mark 35 could also be issued as B.L.&P. or as B.L.&T. for target practice.  Projectiles that used MT or PD nose fuzes had an instantaneous contact type base fuze while a blind plug was used in place of the base fuze for those projectiles using VT nose fuzes.  The AAC Mark 47 was designed as a heavier projectile using new, lighter weight fuzes so as to maintain the same overall projectile weight.  However, the fuzes never appeared, so only a few thousand of the Mark 47 projectiles were manufactured.  Window and White Phosphorous (WP) rounds were available, many as special Mods of the Illumination Mark 30, Mark 44 and Mark 45 projectile bodies.  Chaff rounds were available for jamming different radar types.  Chaff Load Mark 15 was for X-band while Chaff Load Mark 21 was intended for S-band.  Chaff projectiles used a MT nose fuze that triggered a small ejection charge and the loads were dispensed through the base of the projectile.

2) Outfits listed are the design figures.  Pre-war destroyers normally carried about 100 to 150 rounds per gun plus 100 illumination rounds per ship with the balance carried in magazines on Destroyer Tenders (AD).  After 1940, outfits for most destroyers were increased to the design figure plus about 200 illumination rounds per ship.  As the war went on, ammunition stowage on new designs was increased where possible.  Some examples:  Late war Fletcher (DD-445) class carried 525 rounds per gun in magazines plus 50 ready rounds per gun.  Late war A.M. Sumner (DD-692) class carried 422 rounds per gun in magazines plus 50 ready rounds per gun.  The A.M. Sumner class also carried 292 illumination rounds per ship in magazines plus 48 ready illumination rounds per ship.  However, the stowage for pre-war destroyers could not be so greatly increased.  For example, the Farragut class destroyer USS Aylwin (DD-355) had about 250 rounds per gun in magazines plus 50 ready rounds per gun in 1944.  The rebuilt USS Selfridge (DD-357), which had traded her eight SP guns for five DP guns after receiving torpedo damage in 1943, carried about 260 rounds per gun in magazines and 43 ready rounds per gun plus a total of 85 illumination rounds in 1944.  This large increase in ammunition weight resulted in destroyers losing two to four knots in maximum speed from the design specifications.  By 1945, the new battleships in their magazines carried 500 rounds per gun, primarily AA Common and AA VT, plus 40 special types per gun.  In addition, they had 55 ready rounds per gun.  Ready rounds for all ships were stored in handling rooms usually located directly below each mount.

3) Outfits for most ships during the early part of World War II consisted primarily of AA Common plus illumination rounds.  As noted above, changing the nose fuze type allowed these rounds to be used as AAC or as HC.  The Porter (DD-356) and Somers (DD-381) classes as originally built with SP guns carried mostly Common rounds, but they did carry a few AA Common rounds which were intended for use against torpedo bombers and other low-flying planes.  Starting in late 1942, AA VT projectiles were introduced and became increasingly available as the war went on.  By the middle of 1944, most front-line ships had about three AA VT rounds for every one AA Common round.  The usual practice was to fire this ratio at attacking aircraft.  The smoke puffs created by the time-fuzed AA Common rounds allowed the fire control officers to assess and correct the accuracy of the firing control solution and also provided target guidance for the gun crews of the 40 mm and 20 mm AA guns.  VT fuzing reduced roughly in half the number of rounds fired per aircraft shot down.  A notable success with VT ammunition was that of USS Abercrombie (DE-343) which shot down a Ohka (Baka) rocket glider bomb in May 1945, firing only two rounds.

4) Rounds were normally 5.25crh.  Some rounds may have been slightly boat-tailed.

5) The cartridge cases were sealed with cork plugs which extended about 2.5 in (6.4 cm) past the mouth of the case.

6) The Rocket Assisted Projectile (RAP) round was developed during the 1960s.  The rocket engine burned for 40 seconds.

7) Projectiles leave the barrel rotating at about 208 RPS.

8) The illumination rounds burn for approximately 50 seconds.

9) In the early 1950s an anti-submarine projectile designated as EX-30 was under development.  This was a long, fin-stabilized projectile weighing 75.0 lbs. (34.0 kg) and with a muzzle velocity of 300 to 500 fps (91 to 152 mps) intended to be used against submarines within 2,000 yards (1,830 m).  The propellant was inserted between the shrouded tail fins.  Initial testing in 1952 was successful but the project was not further developed.

10) Bourrelet diameter was 4.985 inches (12.66 cm).

11) Cartridge Case Mark 5 Modified was used for Reduced Charges and could hold up to 9.0 lbs. (4.1 kg) of propellant.

12) Some SPD propellant charges had flashless pellets added which gave them a "reduced" flash.

13) Post-war, Brazil, Spain and Turkey set up manufacturing facilities to produce projectiles to USN specifications.

With AAC Mark 49
55.18 lbs. (25.03 kg)
MV of 2,500 fps (762 mps)
With WP Mark 46
53.00 lbs. (24.0 kg)
MV of 2,600 fps (792 mps)
10 degrees
9,506 yards (8,692 m)
9,800 yards (8,960 m)
15 degrees
11,663 yards (10,665 m)
11,900 yards (10,880 m)
20 degrees
13,395 yards (12,248 m)
13,650 yards (12,480 m)
25 degrees
14,804 yards (13,537 m)
15,050 yards (13,760 m)
30 degrees
15,919 yards (14,556 m)
16,200 yards (14,810 m)
35 degrees
16,739 yards (15,298 m)
17,050 yards (15,590 m)
40 degrees
17,240 yards (15,764 m)
17,450 yards (15,960 m)
45 degrees
17,392 yards (15,903 m)
17,575 yards (16,070 m)
AA Ceiling
37,200 feet (11,887 m)

1) At a new gun muzzle velocity of 2,600 fps (792 mps), the AAC Mark 49 had a maximum range of 18,200 yards (16,640 m).

2) This weapon had a maximum slant range of 12,000 yards (11,000 m).

3) RAP round had a maximum range of 23,770 yards (21,735 m).

4) Time of flight for AAC projectile with MV = 2,500 fps (762 mps):
   5,000 yards (4,570 m):  8.0 seconds
   10,000 yards (9,140 m):  22.0 seconds
   15,000 yards (13,720 m):  43.0 seconds
   17,270 yards (15,790 m):  68.8 seconds

Armor Penetration with 55.18 lbs. (25.0 kg) Special Common Shell
Side Armor
Deck Armor
4,000 yards (3,660 m)
5.0" (127 mm)
5,400 yards  (4,940 m)
4.0" (102 mm)
7,400 yards (6,770 m)
3.0" (76 mm)
11,000 yards (10,060 m)
2.0" (51 mm)
13,800 yards (12,620 m)
1.0" (25 mm)

1) These figures are taken from USN armor penetration curves published in 1942.

2) It should be noted that US ships during World War II carried only small quantities of Special Common ammunition as the AA Common projectiles were considered to be more useful against a greater variety of targets.

Armor Penetration with 55.18 lbs. (25.0 kg) AA Common Shell
Side Armor
Deck Armor
10,000 yards (9,140 m) 
1.5" (38 mm)

1) Data from "Destroyer Weapons of World War 2."

2) As noted above, AA Common was greatly used during World War II.

Mount / Turret Data
(see Notes 1 and 25)
Single Open or Open-back Shield Pedestal Mounts
    Farragut (5) and Mahan (5):  Mark 21
    Gridley (2), Dunlap (3) and Bagley (2):  Mark 21 [stern mounts]
    Wichita (4):  Either Mark 21 or Mark 24
    Yorktown (8) and Enterprise (8):  Mark 21 Mod 16
    Wasp (8):  Mark 24 Mod 1
    Hornet (8):  Mark 24 Mod 2
    Independence (2) and Essex (4):  Mark 24 Mod 11

    Brazil:  Marcilio Dias (4):  appear to be Mark 21
    Brazil:  Acre (2):  appear to be Mark 21 [stern mounts]

Single Enclosed Base Ring Mounts
    Gridley (2) and Dunlap (2):  Mark 25 [bow mounts]
    Wichita (4):  Mark 30 Mods 0, 4 and 5
    Bagley (2) and Benham (2):  Mark 30 Mods 0 and 2 [bow mounts]
    Sims (3):  Mark 30 Mods 0 and 2 [mounts 1, 2 and 5]
    Benson (3) and Gleaves (3):  Mark 30 many different Mods [mounts 1, 2 and 5]
    Fletcher (5):  Mark 30 many different Mods
    Rudderdow (2) and John C. Butler (2):  Mark 30 Mod 42

    Britain:  HMS Delhi (5):  Mark 30 Mods 6, 7 and 8

    Brazil:  Acre (2):  appear to be either Mark 25 or Mark 30 [bow mounts]

Single Open Base Ring Mounts
    Benham (2):  Mark 30 Mod 1 [stern mounts]
    Sims (2), Benson (2) and Gleaves (2):  Mark 30 Mod 1 [mounts 3 and 4]
    Escort Carriers (1 or 2):  Mark 30 Mod 80

      Ameer (2):  Probably Mark 30 Mod 80, but possibly Mark 37 Mod 2
      Assistance (USN AR-17 class) (1):  Mark 30

Twin Enclosed Base Ring Mounts
    Porter (4) and Somers (4):  Mark 22
    North Carolina (10) and South Dakota (8) or (10):  Mark 28 Mod 0
    Iowa (10):  Mark 28 Mod 2
    St. Louis (4), Atlanta (8), Oakland (6) and Juneau (ii) (6):  Mark 29
    Des Moines (6), Baltimore (6), Oregon City (6), Cleveland (6) and Fargo (6):  Mark 32 Mod 0
    Essex (4):  Mark 32 Mod 0, Mod 2 and Mod 4
    Alaska (6):  Mark 32 Mod 4
    A.M. Sumner (3) and Gearing (3):  Mark 38

Postwar Construction
    Single Open:  Albany (2):  Mark 30
    Single Enclosed:  Brooke (1), Garcia (2), Long Beach (2) and USCG Hamilton (1):  Mark 30
    Twin Enclosed:  Danish Peder Skram (2), Italian Impetuoso (2) and Italian San Giorgio (3):  Mark 38

(see Note 13)
Single Open Pedestal Mounts
    Mark 21:  29,260 lbs. (13,272 kg)
    Mark 24:  31,200 lbs. (14,152 kg)

Single Open Base Ring Mounts
    Mark 30 Mod 1:  33,500 lbs. (15,195 kg)
    Mark 37:  34,700 lbs. (15,740 kg)

Single Enclosed Base Ring Mounts
    Mark 25:  42,000-44,900 lbs. (19,051-20,367 kg)
    Mark 30 Mod 0:  40,900 lbs. (18,552 kg)
    Mark 30 Mod 41:  41,400 lbs. (18,779 kg)

Twin Enclosed Base Ring Mounts
    Mark 22 Mod 0:  75,250 lbs. (34,133 kg)
    Mark 28 Mod 0: 156,295 lbs. (70,894 kg)
    Mark 28 Mod 2:  170,635 lbs. (77,399 kg)
    Mark 29 Mod 0:  108,000 lbs. (49,000 kg)
    Mark 32 Mod 0:  105,600 lbs. (47,899 kg)
    Mark 32 Mod 4:  120,369 lbs. (54,598 kg)
    Mark 38 Mod 0:  95,700 lbs. (43,409 kg)

(see Notes 3 and 14)
Single Mounts
   All with the following exceptions:  -15 / +85 degrees
   Mark 24 Mod 11:  -10 / +85 degrees
   Mark 30 Mod 51:  -5 / +85 degrees
   Mark 30 Mod 80:  -15 / +27 degrees

Twin Mounts
   All except Mark 22:  -15 / +85 degrees
   Mark 22:  -10 / +35 degrees

Elevation Rate Single Mounts
    Mark 24:  15 degrees per second
    Mark 25:  15 degrees per second
    Mark 30 with GE controls:  15 degrees per second
    Mark 30 with Ford controls:  18 degrees per second
    Mark 37:  15 degrees per second

Twin Mounts
    Mark 22:  11.6 degrees per second
    Mark 28:  15 degrees per second

Train Destroyers:  Depending upon position, arc of 284 degrees up to an arc of 330 degrees
Cruisers and Capital ships:  Bow and stern mounts:  about -150 / +150 degrees
Cruisers and Capital ships:  Broadside mounts:  about -80 / +80 degrees
Train Rate Single Mounts
    Mark 24:  28.75 degrees per second
    Mark 25:  28.7 degrees per second
    Mark 30 with GE controls:  28.75 degrees per second
    Mark 30 with Ford controls:  34 degrees per second
    Mark 37:  30 degrees per second

Twin Mounts
    Mark 22:  14.7 degrees per second
    Mark 28:  25 degrees per second

Loading Angle
(see Note 15)
Gun recoil
(see Note 12)
All mounts except Mark 22:  15 in  (38 cm)
Mark 22:  19 in (48 cm)

1) The mounting types, designations and quantities shown in this table are primarily for warships "as commissioned" and are mainly the result of my research for a Technical Board essay on USN naval gun mounting production during World War II.  These quantities, Mark and Mod numbers may not be in agreement with some of the published works listed below, but I believe them to be correct.  Besides those ships listed above, this weapon was extensively used on auxiliaries and merchant ships as well as on US Coast Guard ships.

2) The Mark 21 pedestal mount was at the limit of turning masses that could be easily manhandled.  To get to this weight, BuOrd sacrificed shields and ammunition hoists and accepted the resulting lower rate of fire.  Ammunition for these mounts was fed from deck mounted scuttles, from which rounds could be passed to a rack of fuze-setters located on the rotating mount.  Mark 21 bow mounts on destroyers had simple open-back shields while the stern mounts were left open and unshielded.  The bow shields for these mounts were notable for having a bulge on the left side in order to accommodate the fuze-setter rack.  All Mark 21 mountings were originally manually trained and elevated, but RPC was added during the war to most ships with 1.5 hp elevating and 2 hp training motors.

3) The Mark 22 twin mount used on the Porter (DD-356) and Somers (DD-381) destroyer classes was the only SP mounting ever developed for these weapons.  Their low maximum elevation of +35 degrees of elevation was adopted mainly as a weight savings, as it was calculated that these ships would only be able to carry six DP guns rather than the eight SP guns that they actually did carry.  The Mark 22 mounting used a 15 hp training motor and a 5 hp elevating motor.  Most of the destroyers with these mountings lost their No. 3 mount as weight compensation for growth in other areas and those destroyers modernized during World War II had all of their SP mountings replaced with two twin Mark 38 DP mountings and one single Mark 30 DP mounting.

4) The Mark 24 was an improved pedestal mounting that had RPC as designed and was powered by a single 5 or 10 hp motor which worked both elevation and train, along with a 5 or 7.5 hp motor for ramming.  Ammunition supply was in the fixed structure for these mountings.  The Mark 24 mountings were considered to be near the maximum weight possible that would still allow them to be hand worked in an emergency.  Many of these mountings had the familiar fuze-setter racks on the platform, controlled by their Mark 33 and Mark 37 Fire Control Systems (FCS).

5) The Mark 25 was the prototype enclosed base ring mounting.  As best as I have been able to determine, these were only used for the bow mounts on the four destroyers of the Gridley (DD-380) class and for the bow mounts on USS Dunlap (DD-384) and USS Fanning (DD-385).  As such, these last two ships formed a sub-class within the Mahan (DD-364) class, as all other ships of the Mahan class used Mark 21 pedestal mounts in all positions.  Some of these Mark 25 mounts appear to have been replaced with Mark 30 enclosed base ring mounts during the war.

6) The Mark 30 mountings made up by far the majority of single mountings built during the war.  The Mark 30 ran up to Mod 86, with Mod 0 being the original enclosed mounting and Mod 1 being the original open mounting.  The Mark 30 Mod 0 enclosed base ring mounts were first introduced on USS Wichita (CA-45).  There were also semi-enclosed mounts which had the upper half of the shield removed as a weight savings but having a canvas cover to protect the interior of the mount.  Many of the Mark 30 modifications were trivial in nature.  For example, USS Fletcher (DD-445) used Mod 16 in positions 1 and 5, Mod 19 in position 2, Mod 30 in position 3 and Mod 31 in position 4.  The differences were mainly related to the elevation and training limitations inherent in the different mounting positions.  Escort Carriers (CVE) completed during the war used Mark 30 Mod 80 which was a simplified base ring mounting which lacked shields, axial hoists and RPC.  The maximum elevation of this Mod was restricted to +27 degrees as it was installed under the flight deck overhang.  The single open Mark 30 Mod 48 and Mark 30 Mod 51 mountings were simplified base-ring types for auxiliaries and merchant ships and lacked integral shell hoists.  Trunnion height was 58.0 inches (147 cm) above the loading platform.  55 inches (140 cm) is considered the maximum desirable trunnion height when firing at low elevations for a 50 - 55 lbs. (22.7 - 24.9 kg) projectile.

7) Almost all Mark 25 and Mark 30 base ring single mounts had an integral shell hoist on the axis of the mounting which allowed shells to be passed directly to the gun at any angle of train.  Fuzes were automatically set as the shells traveled up the hoist.  Cartridges were passed up to the gun through a scuttle also on the rotating mass.  These base ring mounts with integral shell hoists and cartridge scuttles had the advantage that projectiles and cartridges were presented to the loaders at exactly the same position and orientation regardless of the mount's elevation or training and thus simplified and sped up the loading procedure.  Both the shell hoist and the cartridge scuttle were on the left side of the mount.  Mark 25 and enclosed Mark 30 base ring mountings used a single 10 hp motor to work both elevation and train, a 7.5 hp motor for the hoists and a 7.5 hp or 5 hp motor for ramming.

8) All twin SP and DP mounts were base ring types and were generally similar to single enclosed base ring mounts.  Twin mounts differed from single mounts in that there were twin powder hoists for the cartridges on the rotating structure as well as twin shell hoists.  The hoists for the right gun came up through the deck on the left side of the gun while those for the left gun came up on the right side of the gun.  Twin mounts took about 27 crewmen in the mount itself and in the upper handling room.  Additional personnel were required in the lower handling room during sustained firing periods.

9) All twin DP mountings were equipped with RPC gear and powered by electric motors through hydraulic gear.  Training was by a 4 hp motor while the guns were elevated by a 7.5 or 10 hp motor.  Each gun had a 7.5 or 10 hp motor for the hoists and a 5 or 7 hp motor for the rammer.

10) The Mark 22 SP twin mounting had the gun axes 72 inches (183 cm) apart.  All DP twin mountings had the gun axes 84 inches (213 cm) apart.

11) The Mark 37 was a much simplified single mounting developed by Northern Ordnance, Inc. that was primarily intended for merchant ships and auxiliaries.  This mounting lacked hoists and shields and had a simplified sighting system as it was designed to be used only in local control.  Over 3,600 were built during the war, with about 1,600 of these being used on merchant ships.

12) The maximum, metal to metal recoil distance for most mountings was 19 inches (48 cm).

13) The major differences in weight for enclosed mountings was from the thickness of the shield, which ran from 0.25" (0.64 cm) for destroyer mountings up to 2.5" (6.4 cm) on battleships.

14) All single and twin DP mounting types were designed to allow +85 degrees of positive elevation, with the exception of those altered for specific applications, such as the Mark 30 Mod 80, which was restricted to +27 degrees to allow installation on escort carriers under the flight deck overhang.  Most DP mountings had a maximum negative elevation of -15 degrees, but a few Mods were restricted to -7 or -10 degrees for application reasons.

15) Ramming was power-worked on all mountings and was either pneumatic or by a 5 hp electric motor with hydraulic drive.  This allowed any-angle loading and thus a sustained high rate of fire even at high elevations.  In an emergency, guns could be manually rammed but this could not be done when the gun was at high elevations.  The Gunnery Officer aboard USS Enterprise (CV-6) reported after the Battle of the Eastern Solomons that two of his guns lost power during the battle and that manual ramming reduced their ROF by more than half.  However, this same report credits the 5"/38 (12.7 cm) guns on this carrier with three dive bombers definitely shot down and with others set on fire or forced to abort for a total expenditure of only 97 rounds.

16) Destroyers of the Gridley (DD-380), Dunlap (DD-384) and Bagley (DD-386) classes had something of a mixed battery, as they had enclosed base ring mountings on the bow, but open pedestal mountings on the stern.  USS Benham (DD-397) was the first destroyer with a uniform battery of base ring single mountings, although the stern mounts were still of the open type.  It was not until the larger Fletcher (DD-445) class that destroyers had all of their guns in enclosed mountings.

17) Most of the five-gun destroyers built prior to 1942 had mount No. 3 removed during the war as weight compensation for growth in other areas, such as ASW equipment, light AA and electronic installations.  Some four-gun destroyers lost one or both gun shields on the stern mountings as weight compensation.  The Sims (DD-409), Benson (DD-421) and Gleaves (DD-423) classes started out with three enclosed mountings (mounts 1, 2 and 5) and two open mountings (mounts 3 and 4).  After experience with an Atlantic winter in 1941-42, the open mounts were replaced with open-top, semi-enclosed versions with a canvas cover for weather protection.  Later, as additional weight compensation, mount 3 was removed from these ships.  During her refit in the summer of 1945, USS Shaw (DD-373) was found to be significantly overweight, probably because of the structural strengthening she received during her reconstruction in 1942 to repair damage from the Pearl Harbor attack.  As a result, she was reduced to three 5" (12.7 cm) guns in order to allow for additional light AA guns.  All of her torpedo tubes were also removed during this refit.

18) Some older ships were rearmed with these guns during the war.  For example, in 1942 USS Saratoga (CV-3) was rearmed with four 5"/38 (12.7 cm) Mark 32 Mod 2 twin mountings and eight 5"/38 (12.7 cm) Mark 30 Mod 33 single mountings.  The rebuilt or refitted battleships Nevada (BB-36), Pennsylvania (BB-38), Tennessee (BB-43), California (BB-45), Maryland (BB-46) and West Virginia (BB-48) had their older 5"/51 (12.7 cm) and 5"/25 (12.7 cm) guns replaced with eight twin 5"/38 (12.7 cm) mountings.  USS Idaho (BB-42) was given ten single 5"/38 (12.7 cm) Mark 30 mountings in 1944.  USS Savannah (CL-42) had her eight single 5"/25 (12.7 cm) guns replaced with four twin 5"/38 (12.7 cm) mountings in 1944.

19) USS Yorktown (CV-5) and Enterprise (CV-6) were originally designed with eight Mark 21 Mod 1 pedestal mounts.  During construction, it became apparent that there was not enough clearance around the deck edge for this Mod.  For that reason, the mounts were redesigned to have a lower loader's platform and then designated as Mark 21 Mod 16.  Yorktown was sunk with these mounts, but Enterprise had hers replaced with Mark 24 Mod 11 mounts during her overhaul at Puget Sound in 1943.  Sister-ship Hornet (CV-8) was completed with eight Mark 24 Mod 2 mounts.  These were altered to Mod 6 sometime prior to September 1942.

20) Most USS Essex (CV-9) class carriers were completed with four Mark 32 twin mounts, mainly Mods 0, 2 and 4, and four Mark 24 Mod 11 pedestal single mounts.  Post-war, a few of these ships had their pedestal mounts replaced with Mark 30 base ring open mountings for reasons that are not clear.  By the early 1960s, all of the twin mountings had been removed from those carriers still in commission.  A few of these carriers were modified by this time such that they now carried eight single mountings, two on each corner.  The batteries were reduced during the 1960s, with Essex (CVS-9) carrying four Mark 30 Mod 86 mounts in February 1968, Yorktown (CVS-10) had four Mark 24 Mod 11 mounts as of November 1964, Ticonderoga (CVS-14) had three Mark 24 Mod 11 as of June 1973 and Randolph (CVS-15) carried three Mark 24 Mod 11 and one Mark 24 Mod 6 as of September 1966.

21) USS Independence (CVL-22) was completed with two Mark 24 Mod 11 mounts, but these were removed soon after commissioning at the CO's request.  No other carrier of this class was commissioned with these guns.

22) Some destroyer escorts had the rear of the shield of their bow 5"/38 (12.7 cm) mounting cut off at an angle to allow clearance for Hedgehogs firing directly ahead.

23) HMS Delhi replaced her six 6"/45 (15.2 cm) Mark XII guns with five enclosed Mark 30 mounts which were installed in positions 1, 2, 4, 5 and 6.  Her forward, midships and after magazines were converted to handle 5" (12.7 cm) ammunition.  The magazine formerly used for mount 3 was converted to oil tankerage.  Standard US handling rooms were fitted under the mounts, with dredger hoists in each handling room used to bring up ammunition from the magazines.  British fire control equipment was removed and Delhi was given two Mark 37 GFCS to control these guns during her refit.  Cabling and other electrical and structural work to accommodate British radar equipment was performed in the USA, but no radars were actually fitted until Delhi returned to Britain where Type 285 fire control radars were fitted to the directors.

24) The Brazilian Marcilio Dias class were patterned after the USS Mahan (DD-364) class.  The Brazilian Acre class were originally patterned after the British G-H class destroyers, but the use of USN equipment and weapons pushed the design more towards that of the USS Gridley (DD-380) class.  The gun in No. 2 position on most of the Acre class was replaced with a twin 40 mm Bofors mounting during refits in the early 1960s.

25) According to Danish Naval History, these guns when used on the Peder Skram class frigates were designated as 127 mm Gun K M/60 LvSa2.  These ships lost one of their Mark 38 mountings in order to fit Harpoon Launchers during the 1980s.

26) USCG Hamilton (WHEC-715) was rebuilt starting in 1985 and had her 5"/38 (12.7 cm) gun replaced with a 76 mm (3") Mark 75.

27) Post-war, most of the Fletcher, A.M. Sumner and Gearing classes retained in commission lost one of their bow 5"/38 (12.7 cm) mountings in order to install Hedgehog or Weapon Able/Alpha ASW mountings in its place.  In addition, many Fletcher class destroyers lost their amidships 5"/38 (12.7 cm) mounting as weight compensation for additional electronics.  Also notable was USS Gyatt (DDG-1, ex-DD-712), a Gearing class destroyer which traded her stern 5"/38 (12.7 cm) mounting for a twin Terrier missile launcher.  In contrast, USS Carpenter (DDK-825) was originally commissioned in 1949 with two twin 3"/50 (7.62 cm) mountings, was rearmed during the early 1950s with two twin 3"/70 (7.62 cm) mountings but finished out her career in the 1960s with a single twin 5"/38 (12.7 cm) Mark 38 mounting.

28) The six Cleveland class cruisers were converted during the 1950s to Terrier or Talos missile cruisers had their two stern 6"/47 (15.2 cm) mountings and three stern 5"/38 (12.7 cm) mountings removed.  Four of these cruisers were further modified into fleet flagships and had one of their bow 6"/47 (15.2 cm) and two bow 5"/38 (12.7 cm) removed in order to fit flag and communication spaces.  The Baltimore class cruisers USS Boston (CA-69) and USS Canberra (CA-70) had their stern 8"/55 (20.3 cm) and one 5"/38 (12.7 cm) mounting removed when they were converted converted into Terrier missile cruisers during the 1950s.  Two Baltimore class and one Oregon City class cruisers were more heavily modified into all-missile cruisers of the Albany (CG-10) class and had all of their 8"/55 (20.3 cm) and 5"/38 (12.7 cm) mountings removed during their conversions.  Later they had two single 5"/38 (12.7 cm) Mark 30 open mountings added amidships during the 1960s following a failure to successfully launch missiles during a demonstration.  This failure also led to USS Long Beach (CG-9) adding two enclosed 5"/38 (12.7 cm) Mark 30 mountings amidships at the same time, which were removed during modernization in the 1980s.  All of these gun mountings were of limited use as they had modest fire control installations.  USS St. Paul (CA-73) had her bow 5"/38 (12.7 cm) mounting removed in the early 1960s in order to fit additional staff accommodations.

29) During their modernizations in the early 1980s, the Iowa (BB-61) class battleships had four of their twin 5"/38 (12.7 cm) mountings removed in order to fit Harpoon and Tomahawk missile launchers.

30) In May 1943 the French proposed that the incomplete battleship Jean Bart be finished in a US yard and submitted two designs to the USN for review.  The secondary battery for these proposals consisted of fifteen and seventeen 5"/38 (12.7 cm) Mark 32 twin mountings.  Additional detail on this proposal can be found on the French 340 mm datapage.

Click here for a description of what it was like to crew these guns
Data from
"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 14" article in "Warship Volume VIII" both by John Campbell
"Joining the War at Sea 1939 - 1945" by Franklyn E. Dailey Jr., Capt. USNR (Ret.)
"The Naval Institute Guide to World Naval Weapon Systems 1991/92", "US Aircraft Carriers:  An Illustrated Design History," "US Battleships:  An Illustrated Design History", "US Cruisers:  An Illustrated Design History", "US Destroyers:  An Illustrated Design History", "The American 5inch/38 Dual Purpose Gun" article in "Warship Volume II" and "US Naval Weapons" all by Norman Friedman
"Jane's Ammunition Handbook:  Ninth Edition 2000-2001" edited by Terry J. Gander and Charles Q. Cutshaw
"Destroyer Weapons of World War 2" by Peter Hodges and Norman Friedman
"Battleships:  United States Battleships, 1935-1992" by W.H. Garzke, Jr. and R.O. Dulin, Jr.
"French Battleships:  1922 - 1956" by John Jordan and Robert Dumas
"U.S. Navy Bureau of Ordnance in World War II" by Lt. Cmdr. Buford Rowland, USNR, and Lt. William B. Boyd, USNR
"US Warships of World War II" by Paul Silverstone
"Little Ship, Big War:  The Saga of DE-343" by Edward P. Stafford
"Battleships" by Paul Stillwell
"Iowa Class Battleships" by Robert F. Sumrall
"Destroyers of World War Two" and "Cruisers of World War Two" both by M.J. Whitley
"Nomenclature of USN Aircraft Carrier Gun Mounts" by Christopher C. Wright, a letter published in Warship International No. 2, 1998
"Naval Ordnance and Gunnery - 1952" Navpers 16116-B
"5-inch Gun Mounts - Pedestal Types - Ordnance Pamphlet No. 700" by Bureau of Ordnance
"Ammunition:  Instructions for the Naval Service:  Ordnance Pamphlet 4 - May 1943" by Department of the Navy
"5-inch Gun Mounts - Base Ring Types - Mark 30 and Mark 30 Modifications - Ordnance Pamphlet No. 735" by Bureau of Ordnance
"U.S. Explosive Ordnance:  Ordnance Pamphlet 1664 - May 1947" by Department of the Navy
USS Enterprise (CV-6) Gunnery Officer's Action Report for the Battle of the Eastern Solomons
"5-Inch Anti-Submarine Projectile EX-30" by R.D. Cromwell, U.S. Naval Proving Ground, Dahlgren, Virginia, Report No. 1044
"Ordnance Pamphlet 127:  United States Naval Guns, Their Marks and Modifications April 1942" at Gene Slover's US Navy Pages
Special help from Leo Fischer
Off-Site Resources

Operating Instructions for Five Inch, 38 Caliber, Gun Crews on the HNSA Website

Page History

27 November 2008 - Benchmark
25 January 2009 - Added information on British use
20 September 2009 - Added information for mounts on Hornet (CV-8) in 1942 and on Essex class (CVS-9) post-war
22 December 2009 - Added note on proposed Jean Bart reconstruction
14 January 2011 - Added information on USS Albany and USS Long Beach mountings
27 February 2011 - Additional information on projectiles, including dyes and Chaff
13 October 2011 - Corrected typographical errors, added Mark 30 trunnion height
02 May 2012 - Added comment regarding USS Carpenter rearmament, added comments regarding missile cruiser conversions
17 October 2012 - Modified Mount / Turret note about HMS Delhi
24 February 2013 - Added rearmament data