United States of America
5"/50 (12.7 cm) Mark 5 and Mark 6
Updated 12 February 2008
This was the first USN long-barrel 5-inch (12.7 cm) gun and was used as the secondary battery on battleships and cruisers in the early part of the twentieth century.  It was considered to be an interim design and was later replaced on new construction by the more powerful 5"/51 (12.7 cm).

During World War II, these guns were used to arm some cargo ships, store ships and unclassified auxiliaries (IX).  They were also used in emergency coastal defense batteries.

The Mark 5 was a built-up gun while the Mark 6 was to a simpler design, replacing the earlier gun's jacket, chase hoop and locking ring with a single jacket.  Both Marks used a side-swinging Welin breech block with Vickers breech mechanisms.
WNUS_5-50_mk5_St_Louis_pic.jpg

 Starboard waist gun on S.S. Saint Louis in December 1917
Not entirely certain, but this appears to be a 5"/50 (12.7 cm) Mark 6 on a Mark 9 mounting
U.S. Naval Historical Photograph # NH 89499
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Click here for additional pictures
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Gun Characteristics
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Designation 5"/50 (12.7 cm) Marks 5 and 6
Ship Class Used On Delaware (B-28), Denver (C-14) and Chester (CS-1) classes
New York (ACR-2) and New Orleans (CL-22) classes as rearmed
Date Of Design about 1900
Date In Service 1904
Gun Weight N/A
Gun Length oa N/A
Bore Length 250 in (6.350 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist Mark 5:  Increasing RH 0 to 1 in 25 at the muzzle
Mark 6:  Uniform RH 1 in 25
Chamber Volume N/A
Rate Of Fire about 6 - 8 rounds per minute
Note:  New York was rearmed with Mark 6 guns.  I lack data as to which Mark was used for other warships.
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Ammunition
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Type Bag
Projectile Types and Weights AP - 50 lbs. (22.7 kg)
AP - 60 lbs. (27.2 kg)
Common Mark 15 Mods 1 through 14 - 50 lbs. (22.7 kg)
Bursting Charge AP - 1.7 lbs. (0.77 kg)
Common Mark 15 - 1.73 lbs. (0.78 kg)
Projectile Length AP - N/A
Common Mark 15 Mods 12 and 14 - 17.0 in (43.2 cm)
Propellant Charge For 50 lbs. (22.7 kg) shells:  21.0 lbs (9.5 kg) SPD or SPDN
For 60 lbs. (27.2 kg) shells:  19.2 lbs (8.5 kg) SPD
Muzzle Velocity For 50 lbs. (22.7 kg):  3,000 fps (914 mps)
For 60 lbs. (27.2 kg):  2,700 fps (823 mps)
Working Pressure For 50 lbs. (22.7 kg):  N/A
For 60 lbs. (27.2 kg):  16.5 tons/in2 (2,600 kg/cm2)
Approximate Barrel Life N/A
Ammunition stowage per gun Delaware:  240 rounds
Others:  N/A
Notes:

1) During World War II, no AP and only Common Mark 15 Mods 12 and 14 were still in general service use.  By 1947, all Common Mods except Mod 14 were considered to be obsolete.

2) Bourrelet diameter was 4.985 inches (12.66 cm).
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Range
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Elevation With 50 lbs. (22.7 kg) Shell
Range @ 25.3 degrees
Probably for a MV of 3,000 fps (914 mps)		 19,000 yards (17,370 m)
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Armor Penetration With 50 lbs. (22.7 kg) Shell
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Range
Side Armor
Deck Armor
9,000 yards (8,230 m)
1.4" (35.6 mm)
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Data from "U.S. Armored Cruisers" and is for Krupp NC armor.
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Mount / Turret Data
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Designation Pedestal Mount
   Delaware (14):  Marks 9 and 12
   Denver (10):  N/A
   Chester (2):  N/A
   New York (10):  N/A
   New Orleans (10):  N/A
Weight  Mark 9:  20,400 lbs. (9,253 kg)
Mark 12:  18,700 lbs. (8,482 kg)
Elevation Mark 9:  -10 / +15 degrees
Mark 12:  -10 / +25 degrees
Elevation Rate Manual operation, only
Train about +150 / -150 degrees
Train Rate Manual operation, only
Gun recoil N/A
Note:  Mark 9 had a trunnion height of 45.5 inches (115.6 cm) but no platform for the loader.  The Mark 12 had the same trunnion height, but also had a platform for the loader 26.25 inches (66.7 cm) below the trunnions.
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Data from
"US Naval Weapons", "US Battleships:  An Illustrated Design History" and "US Cruisers:  An Illustrated Design History" all by Norman Friedman
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"U.S. Explosive Ordnance:  Ordnance Pamphlet 1664 - May 1947" by Department of the Navy