USS Guam - Ship Specifications

USS Guam (CB-2)

Twin 5"/38 cal MK12

Unquestionably the best Dual Purpose gun of WWII, the 5"/38 Mark 12 was designed to replace the mixed batteries of single purpose 5"/25AA and 5"/51SP guns used on WWI-era ships. The 5"/38 DP (12.7 cm) was used as the main batteries of the destroyers and carriers and as the secondary batteries of most cruisers and battleships that served in WWII. It was also used on many auxiliaries and smaller warships as well as US Coast Guard vessels. By the end of WWII, with major advances in radar and the use of VT fused shells, these guns accounted for a growing number of the aircraft shot down in battle. 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 famous weapon that used semi-fixed ammunition. Of autofretted monobloc construction and used a semi-automatic vertical sliding wedge breech mechanism. The gun barrel was secured to the housing by interrupted threads, thus allowing easy barrel replacement. About 8,000 of these weapons were produced between 1934 and 1945.

Technical Data

Gun Characteristics

Designation 5"/38 (12.7 cm) caliber Mark 12

Ship Class Used On First used on USS Farragut DD-348
Used on almost all WWII-era warships Destroyer-sized and larger along with many auxiliaries.

Date Of Design about 1932

Date In Service 1934

Gun Weight 3,990 lbs (1,810 kg) without breech

Gun Length oa 23.8 in (5.683 m)

Bore Length 190 in (4.826 m)

Number Of Grooves 45
Twist 1/30

Length Of Rifling 157.2 in (3.994 m)

Chamber Volume 654 in3 (10.72 dm3)

Rate Of Fire 15 - 20 rounds per minute

Ammunition

Type Semi-fixed

Projectile Types and Weights AP - 54 lbs. (24.5 kg)
AAC Marks 35 and 49 - 55.18 lbs. (25.0 kg)
AAVT Marks 35 and 49 - 54.61 lbs. (24.8 kg)
HC Marks 35 and 49 - 54.3 lbs. (24.6 kg)
WP - 54.39 lbs. (24.7 kg)
Common Marks 38 and 46 - 55.18 lbs. (25.0 kg)

Bursting Charge AAC - 7.6 lbs. (3.4 kg)
AAVT - 7.9 lbs. (3.6 kg)
Common - 2 lbs. (0.9 kg)
HC - 7.6 lbs. (3.4 kg)

Projectile Length 20.75 in (52.7 cm)

Propellant Charge Flashless: 15.5 lbs. (7.031 kg) NF
Non-flashless: 15.4 lbs. (6.986 kg) NC

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

Working Pressure 18.0 tons/in2 (2,835 kg/cm2)

Approximate Barrel Life 4,600 rounds

Magazine capacity per gun Essex (CV-9): 450 rounds
Yorktown (CV-6): 450 rounds
North Carolina (BB-55), South Dakota (BB-57) and Iowa (BB-61): 450 rounds
Cleveland (CL-55), Baltimore (CA-68), Alaska (CB-1): 500 rounds
Atlanta (CL-51): 450 rounds
Allen M. Sumner (DD-)692 and Gearing (DD-710): 360
Fletcher (DD-445): 350 rounds
Benson (DD-421) and Livermore (DD-429): 320 rounds
Most pre-war destroyers: 300 rounds

Notes: 1) Rounds were normally 5.25crh.
2) Some rounds may have been slightly boat-tailed.

Range

Elevation With AAC Mark 49
55.18 lbs. (25.03 kg) With WP Mark 46
53 lbs. (24.04 kg)

10 degrees 9,506 yards (8,692 m) 9,800 yards (8,961 m)

15 degrees 11,663 yards (10,665 m) 11,900 yards (10,881 m)

20 degrees 13,395 yards (12,248 m) 13,650 yards (12,482 m)

25 degrees 14,804 yards (13,537 m) 15,050 yards (13,762 m)

30 degrees 15,919 yards (14,556 m) 16,200 yards (14,813 m)

35 degrees 16,739 yards (15,298 m) 17,050 yards (15,591 m)

40 degrees 17,240 yards (15,764 m) 17,450 yards (15,956 m)

45 degrees 17,392 yards (15,903 m) 17,575 yards (16,071 m)

AA Ceiling 37,200 feet (11,887 m) N/A

Armor Penetration with 54 lbs. (24.5 kg) AP Shell

Range Side Armor Deck Armor

4,000 yards (3,660 m) 5.0" (127 mm) N/A

5,400 yards (4,940 m) 4.0" (102 mm) N/A

7,400 yards (6,770 m) 3.0" (76 mm) N/A

11,000 yards (10,060 m) 2.0" (51 mm) N/A

13,800 yards (12,620 m) N/A 1.0" (25 mm)

Notes:
1) These figures are taken from armor penetration curves published in 1942.
2) It should be noted that US ships did not carry AP ammuntion for these guns during WWII as the HC shell was considered to be more useful against a greater variety of targets.

Mount / Turret Data

Designation Single Open Mounts:
Early destroyers: Mark 21
Improved: Mark 24
Later destroyers: Mark 30 Mod 0
Carriers: Mark 30 Mod 33
Auxiliaries: Mark 30 Mod 48 and Mark 37
Single Enclosed Mounts:
Prototype: Mark 25
Wichita: Mark 30 Mod 0
Early Destroyers: Mark 30 Mod 1
Later Destroyers: Mark 30 Mod 41
Twin Enclosed Mounts:
Porter and Somers: Mark 22
North Carolina and South Dakota: Mark 28 Mod 0
Iowa: Mark 28 Mod 2
Brooklyn and Atlanta (?): Mark 29 Mod 0
Baltimore, Cleveland, Essex: Mark 32 Mod 0
Alaska: Mark 32 Mod 4
A.M. Sumner and Gearing: Mark 38

Weight Single Open Mount:
Mark 21: 29,260 lbs. (13,272 kg)
Mark 24: 31,200 lbs. (14,152 kg)
Mark 30 Mod 0: 33,500 lbs. (15,195 kg)
Single Enclosed Mounts:
Mark 30 Mod 1: 40,900 lbs. (18,552 kg)
Mark 30 Mod 41: 41,400 lbs. (18,779 kg)

Twin Enclosed Mounts:
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)
Destroyer Twin Mount: 95,700 lbs. (43,409 kg)

Elevation Single Mounts except Mark 30/51: -15 / +85 degrees
Single Mount Mark 30/51: -5 / +85 degrees
Twin Mounts except Mark 22: -15 / +85 degrees
Twin Mount Mark 22: -10 / +35 degrees

Elevation Rate Single Mount: 18 degrees per second
Twin Mount: 15 degrees per second

Train about +120 / -120 degrees

Train Rate Single Mount: 34 degrees per second
Twin Mount: 25 degrees per second

Loading Angle Any

Gun recoil Destroyers and smaller ships: 19 in (48 cm) max.
Cruisers and larger ships: 12 in (30.5 cm)

Notes:
1) The Mark 21 and 24 pedestal mounts were at the limit of turning masses that could be easily manhandled. To get to this weight, they sacrificed ammunition hoists and a shield, as well as a high rate of fire. These guns were fed from deck mounted scuttles, from which rounds could be passed to a rack of fuze-setters on the rotating mount. Some Mark 21 mountings had simple open shields added, usually for bow mounts on destroyers.
2) The Mark 30 base ring type first introduced on USS Wichita and USS Craven DD-380 had shell and propellant hoists on the axis of the mount, so that shells and cartridges could be passed directly to the gun at any angle of train. Fuzes were set as the shells traveled up the hoist. These single mounts were considered to be at the maximum weight limit for manhandling.
3) The Mark 30 ran up to Mod 86. Mark 37 was a simplified base-ring type for auxiliaries and merchant ships.
4) Mounts had power ramming, which allowed any-angle loading.

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Gun Characteristics
Designation	5"/38 (12.7 cm) caliber Mark 12
Ship Class Used On	First used on USS Farragut DD-348 Used on almost all WWII-era warships Destroyer-sized and larger along with many auxiliaries.
Date Of Design	about 1932
Date In Service	1934
Gun Weight	3,990 lbs (1,810 kg) without breech
Gun Length oa	23.8 in (5.683 m)
Bore Length	190 in (4.826 m)
Number Of Grooves	45 Twist 1/30
Length Of Rifling	157.2 in (3.994 m)
Chamber Volume	654 in3 (10.72 dm3)
Rate Of Fire	15 - 20 rounds per minute

Ammunition
Type	Semi-fixed
Projectile Types and Weights	AP - 54 lbs. (24.5 kg) AAC Marks 35 and 49 - 55.18 lbs. (25.0 kg) AAVT Marks 35 and 49 - 54.61 lbs. (24.8 kg) HC Marks 35 and 49 - 54.3 lbs. (24.6 kg) WP - 54.39 lbs. (24.7 kg) Common Marks 38 and 46 - 55.18 lbs. (25.0 kg)
Bursting Charge	AAC - 7.6 lbs. (3.4 kg) AAVT - 7.9 lbs. (3.6 kg) Common - 2 lbs. (0.9 kg) HC - 7.6 lbs. (3.4 kg)
Projectile Length	20.75 in (52.7 cm)
Propellant Charge	Flashless: 15.5 lbs. (7.031 kg) NF Non-flashless: 15.4 lbs. (6.986 kg) NC
Muzzle Velocity	New gun: 2,600 fps (792 mps) Average gun: 2,500 fps (762 mps)
Working Pressure	18.0 tons/in2 (2,835 kg/cm2)
Approximate Barrel Life	4,600 rounds
Magazine capacity per gun	Essex (CV-9): 450 rounds Yorktown (CV-6): 450 rounds North Carolina (BB-55), South Dakota (BB-57) and Iowa (BB-61): 450 rounds Cleveland (CL-55), Baltimore (CA-68), Alaska (CB-1): 500 rounds Atlanta (CL-51): 450 rounds Allen M. Sumner (DD-)692 and Gearing (DD-710): 360 Fletcher (DD-445): 350 rounds Benson (DD-421) and Livermore (DD-429): 320 rounds Most pre-war destroyers: 300 rounds
Notes:	1) Rounds were normally 5.25crh. 2) Some rounds may have been slightly boat-tailed.

Range
Elevation	With AAC Mark 49 55.18 lbs. (25.03 kg)	With WP Mark 46 53 lbs. (24.04 kg)
10 degrees	9,506 yards (8,692 m)	9,800 yards (8,961 m)
15 degrees	11,663 yards (10,665 m)	11,900 yards (10,881 m)
20 degrees	13,395 yards (12,248 m)	13,650 yards (12,482 m)
25 degrees	14,804 yards (13,537 m)	15,050 yards (13,762 m)
30 degrees	15,919 yards (14,556 m)	16,200 yards (14,813 m)
35 degrees	16,739 yards (15,298 m)	17,050 yards (15,591 m)
40 degrees	17,240 yards (15,764 m)	17,450 yards (15,956 m)
45 degrees	17,392 yards (15,903 m)	17,575 yards (16,071 m)
AA Ceiling	37,200 feet (11,887 m)	N/A

Armor Penetration with 54 lbs. (24.5 kg) AP Shell
Range	Side Armor	Deck Armor
4,000 yards (3,660 m)	5.0" (127 mm)	N/A
5,400 yards (4,940 m)	4.0" (102 mm)	N/A
7,400 yards (6,770 m)	3.0" (76 mm)	N/A
11,000 yards (10,060 m)	2.0" (51 mm)	N/A
13,800 yards (12,620 m)	N/A	1.0" (25 mm)
Notes: 1) These figures are taken from armor penetration curves published in 1942. 2) It should be noted that US ships did not carry AP ammuntion for these guns during WWII as the HC shell was considered to be more useful against a greater variety of targets.

Mount / Turret Data
Designation	Single Open Mounts: Early destroyers: Mark 21 Improved: Mark 24 Later destroyers: Mark 30 Mod 0 Carriers: Mark 30 Mod 33 Auxiliaries: Mark 30 Mod 48 and Mark 37 Single Enclosed Mounts: Prototype: Mark 25 Wichita: Mark 30 Mod 0 Early Destroyers: Mark 30 Mod 1 Later Destroyers: Mark 30 Mod 41 Twin Enclosed Mounts: Porter and Somers: Mark 22 North Carolina and South Dakota: Mark 28 Mod 0 Iowa: Mark 28 Mod 2 Brooklyn and Atlanta (?): Mark 29 Mod 0 Baltimore, Cleveland, Essex: Mark 32 Mod 0 Alaska: Mark 32 Mod 4 A.M. Sumner and Gearing: Mark 38
Weight	Single Open Mount: Mark 21: 29,260 lbs. (13,272 kg) Mark 24: 31,200 lbs. (14,152 kg) Mark 30 Mod 0: 33,500 lbs. (15,195 kg) Single Enclosed Mounts: Mark 30 Mod 1: 40,900 lbs. (18,552 kg) Mark 30 Mod 41: 41,400 lbs. (18,779 kg) Twin Enclosed Mounts: 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) Destroyer Twin Mount: 95,700 lbs. (43,409 kg)
Elevation	Single Mounts except Mark 30/51: -15 / +85 degrees Single Mount Mark 30/51: -5 / +85 degrees Twin Mounts except Mark 22: -15 / +85 degrees Twin Mount Mark 22: -10 / +35 degrees
Elevation Rate	Single Mount: 18 degrees per second Twin Mount: 15 degrees per second
Train	about +120 / -120 degrees
Train Rate	Single Mount: 34 degrees per second Twin Mount: 25 degrees per second
Loading Angle	Any
Gun recoil	Destroyers and smaller ships: 19 in (48 cm) max. Cruisers and larger ships: 12 in (30.5 cm)
Notes: 1) The Mark 21 and 24 pedestal mounts were at the limit of turning masses that could be easily manhandled. To get to this weight, they sacrificed ammunition hoists and a shield, as well as a high rate of fire. These guns were fed from deck mounted scuttles, from which rounds could be passed to a rack of fuze-setters on the rotating mount. Some Mark 21 mountings had simple open shields added, usually for bow mounts on destroyers. 2) The Mark 30 base ring type first introduced on USS Wichita and USS Craven DD-380 had shell and propellant hoists on the axis of the mount, so that shells and cartridges could be passed directly to the gun at any angle of train. Fuzes were set as the shells traveled up the hoist. These single mounts were considered to be at the maximum weight limit for manhandling. 3) The Mark 30 ran up to Mod 86. Mark 37 was a simplified base-ring type for auxiliaries and merchant ships. 4) Mounts had power ramming, which allowed any-angle loading.