United States of America
8"/55 (20.3 cm) Marks 9, 10, 11, 13 and 14
Updated 23 July 2011
This weapon was used on most US Treaty cruisers and the Lexington class carriers.  None of these ships ever carried the "super-heavy" AP projectiles as their ammunition hoists could not accommodate the longer, heavier round.

As commissioned, the early cruisers had poor dispersion patterns, sometimes as large as 2,000 yards (1,830 m) for a full salvo.  Some of these problems were due to the guns having a very high muzzle velocity and poor shot seating.  Extensive testing to determine the cause of the problems was performed in 1933 at Manila Bay with the assistance of the Coast Artillery and the results sent to BuOrd.  Corrections included reducing the muzzle velocity and relining the barrels.

The guns removed pre-war from USS Lexington (CV-2) and USS Saratoga (CV-3) were reused as coastal artillery on the island of Oahu, Hawaii.

These guns were very heavy when compared to most other 8" (20.3 cm) guns for reasons that are not readily apparent.  Mark 9 was the original design and was used on ships built in the 1920s.  This gun consisted of liner, A tube, jacket, five hoops, three locking rings and a screw box liner.  The Mark 10, which was never built, was a lighter gun constructed of only three hoops.  Mark 11 had only one hoop and was autofretted.  The Mark 13 was the Mark 9 relined with a partially chrome-plated bore.  The Mark 14 was a relined Mark 9 with a fully chrome-plated bore and a smaller chamber.  The Mark 14 was used for most regunnings during World War II.

USS Augusta CA-31
The Marine complement in the 1930s while future Gen. Lewis "Chesty" Puller was commanding
Photograph courtesy of Søren Swigart
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Click here for additional pictures
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Gun Characteristics
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Designation 8"/55  (20.3 cm) Marks 9, 10, 11, 13 and 14
Ship Class Used On Lexington (CV-2), Pensacola (CA-24), Northampton (CA-26), New Orleans (CA-32, 34 and 36 only) and Indianapolis (CA-33) classes
Date Of Design 1922
Date In Service 1930
Gun Weight 30.0 tons (30.48 mt)
Gun Length 449.0 in (11.405 m)
Bore Length 440.1 in (11.179 m)
Rifling Length 373.65 in (9.491 m)
Grooves 64 (?)
Lands N/A
Twist Mark 9 Mods 0 to 3:  Uniform RH 1 in 35
Mark 9 Mod 4:  Uniform RH 1 in 30
Marks 10 and 11:  Uniform RH 1 in 35
Mark 12 Mod 0:  Uniform RH 1 in 35
Mark 12 Mod 1:  Uniform RH 1 in 25
Mark 14:  Uniform RH 1 in 25
Chamber Volume Marks 9, 10, 11 and 13:  5,300 in3 (86.8 dm3)
Mark 14:  4,860 in3 (79.6 dm3)
Rate Of Fire 3 - 4 rounds per minute
Note:  At the Battle of the Java Sea in February 1942, USS Houston (CA-30) was able to maintain a ROF of 5 - 6 rounds per minute during the early part of the battle, possibly through the use of "cue-balling" techniques.
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Ammunition
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Type Bag
Projectile Types and Weights
(see Notes 1 and 2)		 AP Mark 19 Mods 1 to 6 - 260 lbs. (118 kg)
SP Common Mark 17 Mods 1 to 4 - 260 lbs. (118 kg)
Common Mark 14 Mod 1 - 260 lbs. (118 kg)
Common Mark 15 Mod 1 - 260 lbs. (118 kg)
HC Mark 24 Mods 1 to 5 - 260 lbs. (118 kg)
HC Mark 25 Mod 1 - 260 lbs. (118 kg)
Bursting Charge AP Mark 19 - 3.64 lbs. (1.7 kg) Explosive D
SP Common - 10.38 lbs. (4.7 kg) Explosive D
Common Mark 14 - 10.91 lbs. (4.9 kg) Explosive D
Common Mark 15 - 11.46 lbs. (5.2 kg) Explosive D
HC Mark 24 - 21.34 lbs. (9.7 kg) Explosive D
HC Mark 25 - 21.37 lbs. (9.7 kg) Explosive D
Projectile Length
(see Note 4)		 AP Mark 19 - 36.0 in (91.4 cm)
SP Common - 36.0 in (91.4 cm)
Common Mark 14 - 34.0 in (86.4 cm)
Common Mark 15 - 36.0 in (91.4 cm)
HC Mark 24 - 34.56 in (87.8 cm)
HC Mark 25 - 34.61 in (87.9 cm)
Propellant Charge Full Charge - 89 lbs. (40.4 kg) SPD
Full Flashless Charge - 92 lbs. (41.7 kg) SPCG
Muzzle Velocity 2,800 fps (853 mps)
Working Pressure 17.0 tons/in2 (2,680 kg/cm2)
Approximate Barrel Life 715 rounds
Ammunition stowage per gun
(see Note 6)		 150 rounds
Notes:

1) SP Common had a thin hood and a windscreen.  Common had a windscreen but no cap.  HC Mark 25 was designed such that it could be forged from the base end.  Common Mark 14 and Mark 15 shells do not appear to have been in general use during World War II but they still appear in a 1947 Explosive Ordnance publication.

2) HC projectile bodies could be used with Point Detonating (PD) or Mechanical Time (MT) fuzes.  When used with PD fuzes, they were considered to be HC rounds.  When used with MT fuzes, they were considered to be AAC rounds.  MT fuzes were probably set by hand on the loading trays.

3) The Mark 9 originally had a muzzle velocity of 3,000 fps (914 mps), but barrel life was only about 500 rounds and accuracy was poor.

4) Radius of ogive for both AP Mark 19 and HC rounds was 83 inches (211 cm) or about 10crh.  Bourrelet diameter of all rounds was 7.977 inches (20.3 cm).  OP 1664 says that almost all 8" (20.3 cm) rounds were 36.0 inches (91.4 cm) in length.  However, other sources and a careful examination of photographs and sketches lead me to believe that the lengths given above are accurate.

5) The propellant charges were in halves.

6) Most of the 9-gun cruisers as commissioned were to normally carry 100 - 125 rounds per gun with a wartime allowance of 1,400 rounds per ship.  During the early part of the war, the Northampton and Portland classes carried 1,500 rounds per ship, but this was reduced during refits after July 1942 to just over 1,300 rounds in order to allow for added AA weapons.  The New Orleans class was reduced during refits after August 1942 to 125 rounds per gun.
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Range
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Elevation
With 260 lbs. (118 kg) AP
Striking Velocity
Angle of Fall
2.5 degrees
6,000 yards (5,490 m)
2,166 fps (660 mps)
3.0
4.8 degrees
10,000 yards (9,140 m)
1,800 fps (549 mps)
6.4
9.7 degrees
16,000 yards (14,630 m)
1,381 fps (421 mps)
15.4
14.2 degrees
20,000 yards (18,290 m)
1,227 fps (374 mps)
24.4
24.1 degrees
26,000 yards (23,770 m)
1,177 fps (359 mps)
40.4
33.8 degrees
30,000 yards (27,430 m)
1,225 fps (374 mps)
51.4
41.0 degrees
31,860 yards (29,131 m)
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Note:  Time of flight for AP Shell with MV = 2,800 fps (853 mps)
   6,000 yards (5,490 m):  7.3 seconds
   10,000 yards (9,140 m): 13.4 seconds
   20,000 yards (18,290 m):  35.2 seconds
   30,000 yards (27,430 m):  70.6 seconds
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Armor Penetration with 260 lbs. (118 kg) AP Shell
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Range
Side Armor
Deck Armor
9,000 yards (8,230 m)
10.0" (254 mm)
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12,400 yards (11,340 m)
8.0" (203 mm)
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13,500 yards (12,340 m)
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1.0" (25 mm)
16,600 yards (14,630 m)
6.0" (152 mm)
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17,600 yards (16,090 m)
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1.5" (38 mm)
19,500 yards (17,830 m)
5.0" (127 mm)
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21,200 yards (19,390 m)
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2.0" (51 mm)
23,600 yards (21,580 m)
4.0" (102 mm)
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26,400 yards (24,140 m)
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3.0" (76 mm)
29,600 yards (27,070 m)
3.0" (76 mm)
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30,200 yards (27,610 m)
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4.0" (102 mm)
Note:  These figures are taken from armor penetration curves issued in 1942.
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Mount / Turret Data
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Designation
(see Note 2)		 Twin Mounts
   Lexington (4) and Pensacola (2)

Triple Mounts
   Pensacola (2), Northampton (3) and Indianapolis (3)

Triple Turrets
   New Orleans (CA-32, 34 and 36 only) (3)
Weight  Twin Mounts:  187 tons (190 mt)

Triple Mounts:  247 - 250 tons (251 - 254 mt)

Triple Turrets:  294 tons (299 mt)
Elevation -10 / +41 degrees
Elevation Rate about 6 degrees per second
Train about +150 / -150 degrees
Train Rate about 3.5 degrees per second
Gun recoil 29.65 in (75.3 cm)
Loading angle Mounts:  +5 degrees
Turrets:  +9 degrees
Notes:

1) None of these mountings had the guns individually sleeved.

2) There were two different kinds of triple mountings.  The earliest ones were officially classified as "mounts" rather than "turrets," as they had handling rooms directly below the gunhouse rather than a rotating stalk.  The later triple mountings used on New Orleans (CA-32), Astoria (CA-34) and Minneapolis (CA-36) were classified as "turrets" as they had a rotating stalk.  The twin mounts were similar in design to the three-gun mounts.

3) All mountings were electrically powered through hydraulic gear.  The triple turret had a 30 hp training motor and an 18 hp motor that elevated the gun cradle.  Each gun had a 7.5 hp ramming motor and a 7 hp motor for its pusher shell hoist.  Each gun had a shell hoist in the stalk which ran directly from the shell room to the gun breech.  There were two lower powder hoists that ran from the magazine to the handling room and were each powered by a 15 hp motor.  The upper powder hoists were powered by six 1.5 hp motors.  Shells were stored vertically on the fixed structure.

4) The shell and charge hoist arrangements in the earlier triple mountings were similar to the later turrets, but the lower hoists were part of the fixed structure.  The Pensacola class (CA-24) had a 15 hp elevating motor and in all ships the upper charge hoists were powered by 3.5 hp motors while the lower ones were powered by 5 hp motors.  The twin mountings were similar but had a 20 hp training motor and a 10 hp elevating motor.

5) RPC was used in the New Orleans class as built.  RPC was fitted to surviving ships during World War II, except for Salt Lake City (CA-25).

6) The gun axes were about 46 in (117 cm) apart for both the twin and the triple mountings.
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Data from
"Naval Weapons of World War Two" by John Campbell
"US Cruisers:  An Illustrated Design History" and "US Naval Weapons" both by Norman Friedman
"Ship of Ghosts:  The Story of the USS Houston" by James D. Hornfischer
"Round Shot to Rockets:  A History of the Washington Navy Yard and the United States Naval Gun Factory" by Taylor Peck
"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
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Personal reminisces of Vice-Admiral William P. Mack, Gunnery Officer aboard USS John D. Ford (DD-228) during Battle of Java Sea
Special help from Leo Fischer
Page History

12 February 2008 - Benchmark
24 January 2011 - Deleted references to the AP Mark 16
27 April 2011 - Added note about ammunition stowage
23 July 2011 - Added additional information regarding ammunition stowage