United States of America
6"/53 (15.2 cm) Marks 12, 14, 15 and 18
Updated 08 February 2008
An improved weapon used on the Omaha (CL-4) class Light Cruisers and in a wet mount on the "Submarine Cruisers" of the Argonaut (SS-166) and Narwhal (SS-167) classes.  They were also planned for the never-built South Dakota (BB-49) class battleships and Lexington (CC-1) class battle-cruisers.

During initial gunnery trials for USS Trenton (CL-11) on 20 October 1924, two charges of powder in the forward twin mounting were ignited.  Twenty men were in the twin mount of whom four died almost immediately and ten died later from burns and inhalation of flames and gases.  The remaining six were severely injured.  Ensign Henry Drexler and Boatswain's Mate First Class George Cholister were posthumously awarded the US Congressional Medal of Honor for their attempts to prevent the tragedy.

Mark 12 was of built-up construction consisting of A tube, liner, full length jacket, two hoops, one locking ring and a screw box liner.  The Welin breech was a side-swing model with Smith-Asbury mechanism.  The Mark 14 was of autofretted monobloc construction.  Mark 15 was to have been a lighter-weight monobloc but was not built.  Mark 18 was a relined Mark 12 with chrome plating.
WNUS_6-53_mk12_Raleigh_pic.jpg

USS Raleigh CL-7 anchored in San Diego Harbor 21 October 1933
Note that the 6" (15.2 cm) guns were in both twin turrets and single casemate mounts
U.S. Naval Historical Center Photograph # NH 64621
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Click here for additional pictures
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Gun Characteristics
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Designation 6"/53 (15.2 cm) Marks 12, 14, 15 and 18
Ship Class Used On Omaha (CL-4), South Dakota (BB-49), Lexington (CC-1), Argonaut (SS-166) and Narwhal (SS-167) Classes
Date Of Design 1920
Date In Service 1923
Gun Weight 10.11 tons (10.27 mt)
Gun Length oa 325.0 in (8.255 m)
Bore Length 318.0 in (8.077 m)
Rifling Length 265.3 in (6.713 m)
Grooves N/A
Lands N/A
Twist Uniform RH 1 in 35
Chamber Volume 2,100 in3 (34.4 dm3)
Rate Of Fire 6 - 7 rounds per minute
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Ammunition
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Type Bag
Projectile Types and Weights
(see Note 1)		 AP - 105 lbs. (47.6 kg)
SP Common Mark 27 Mods 1 to 8 - 105 lbs. (47.6 kg)
Common Mark 24 Mods 0 to 4 - 105 lbs. (47.6 kg)
HC Mark 34 Mods 1 to 7 - 105 lbs. (47.6 kg)
Illum Mark 22 Mod 1 - 95.40 lbs. (43.3 kg)
Illum Mark 23 Mods 1 and 2 - 96.0 lbs. (43.5 kg)
Bursting Charge SP Common Mark 27 all Mods except 2 and 5 - 2.20 lbs. (1.0 kg) Explosive D
SP Common Mark 27 Mods 2 and 5 - 2.50 lbs. (1.1 kg) Explosive D
Common Mark 24 - 7.08 lbs. (2.6 kg) Explosive D
HC Mark 34 - 13.22 lbs. (6.0 kg) Explosive D
AP - N/A
Projectile Length AP - 22.8 in (58 cm)
SP Common - 27.0 in (68.6 cm)
Common - 27.0 in (68.6 cm)
Propellant Charge 44 lbs. (20.0 kg) SPD
44 lbs. (20.0 kg) SPDN
Flashless - 46 lbs. (20.9 kg) SPCG
Muzzle Velocity AP - 3,000 fps (914 mps)
Common - 3,000 fps (914 mps)
HC - 3,000 fps (914 mps)
Working Pressure 17.5 tons/in2 (2,760 kg/cm2)
Approximate Barrel Life
(see Note 3)		 Mark 12:  400 Rounds
Mark 18:  700 rounds
Magazine capacity per gun Omaha class:  200 rounds
Submarines:  360 rounds
Others:  N/A
Notes:

1) Special Common had a windscreen and a thin cap and the body was strengthened to enhance its armor piercing qualities.  Common Mark 32 had a windshield but no cap.

2) AP, SP Common and HC projectiles were carried by cruisers while Common Mark 24 rounds were carried by submarines.  AP rounds do not appear to have been issued during World War II, SP Common was issued in its place.

3) The effect of HC rounds on barrel life was equivalent to only 0.16 of the AP round while the training round, which had a muzzle velocity of 2,300 fps (701 mps), was 0.13.

4) Bourrelet diameter was 5.985 inches (15.2 cm).
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Range
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Elevation With 105 lbs. (47.7 kg) AP Shell
Range @ 20 degrees 21,100 yards (19,290 m)
Range @ 25 degrees 23,300 yards (21,300 m)
Range @ 30 degrees 25,300 yards (23,130 m)
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Armor Penetration with 105 lbs. (47.6 kg) AP Shell used on Cruisers
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Range
Side Armor
Deck Armor
6,300 yards (5,760 m)
4.0" (102 mm)
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9,000 yards (8,230 m)
3.0" (76 mm)
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13,800 yards (12,620 m)
2.0" (51 mm)
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17,200 yards (15,730 m)
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1.0" (25 mm)
20,800 yards (19,020 m)
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1.5" (38 mm)
23,600 yards (21,580 m)
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2.0" (51 mm)
Note:  These figures are taken from armor penetration curves published in 1942.
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Armor Penetration with 105 lbs. (47.6 kg) Common Shell used on Submarines
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Range
Side Armor
Deck Armor
8,200 yards (7,500 m)
4.0" (102 mm)
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12,200 yards (11,160 m)
3.0" (76 mm)
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17,000 yards (15,540 m)
2.0" (51 mm)
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19,400 yards (17,740 m)
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1.0" (25 mm)
22,600 yards (20,670 m)
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1.5" (38 mm)
Note:  These figures are taken from armor penetration curves published in 1942.
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Mount / Turret Data
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Designation Casemate Mounts
   Omaha (8):  Mark 13
   South Dakota (16) and Lexington (16):  Mark 13 (?)

Twin Mounts
  Omaha (2):  Mark 16

Wet Mount
   Submarines (2):  Mark 15
Weight  Twin Mount:  51.8 tons (52.6 mt)
Casemate Mount:  19.1 tons (19.4 mt)
Submarine Mount:  37,700 lbs. (17,100 kg)
Elevation Twin Turret:  -10 / +30 degrees
Casemate Mount:  -10 / +20 degrees
Submarine Mount:  -10 / +25 degrees
Elevation Rate Twin Mount:  7.6 degrees per second
Casemate and Submarine Mount:  Manual operation, only
Train Twin Mount:  about +150 / -150 degrees
Casemate:  about +75 / -75 degrees
Submarine Mount:  360 degrees
Train Rate Twin Mount:  N/A
Casemate and Submarine Mount:  Manual operation, only
Gun recoil N/A
Note:  Cincinnati (CL-6), Raleigh (CL-7), Detroit (CL-8), Richmond (CL-9) and Marblehead (CL-12) had the after lower casemate guns removed during the 1930s as weight compensation for growth in other areas.  Marblehead had one of these guns remounted in a superfiring position on the after superstructure.  During World War II, the remaining cruisers were reduced to 10 guns by removal of the two after casemate guns and Marblehead lost her centerline gun.  In 1945 Detroit was reduced to eight guns by the removal of her two forward upper casemate guns which were replaced by twin 40 mm mountings.
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Data from
"Naval Weapons of World War Two" by John Campbell
"US Cruisers:  An Illustrated Design History," "US Submarines through 1945:  An Illustrated Design History" and "US Naval Weapons" all by Norman Friedman
"Cruisers of World War Two" by M.J. Whitley
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"U.S. Explosive Ordnance:  Ordnance Pamphlet 1664 - May 1947" by Department of the Navy