United States of America
5"/51 (12.7 cm) Marks 7, 8, 9, 14 and 15
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Britain
5"/51 (12.7 cm) BL Marks VI and VII
Updated 23 February 2013
First introduced as anti-torpedo boat guns in the battleships of the Florida (B-30) and Wyoming (B-32) classes.  Later versions were mounted on almost all battleships built in the 1910s and 1920s and fitted to many smaller warships.  Most versions fired bag ammunition, with the exception of the Mark 9 which was a "wet-gun" for submarine use and used semi-fixed (separate) ammunition.

These guns were also used as coastal artillery, most notably at Wake Island, where they are credited with sinking the Japanese destroyer IJN Hayate.

The US Navy was proud of the performance of this gun, as it had both a high muzzle velocity and good accuracy, important features for an anti-destroyer weapon on capital ships.  As a result of its high muzzle velocity, the danger space for this gun was quite large, actually longer than the range to the target for distances less than 3,000 yards (2,740 m).  This high performance did result in a short barrel life.

In the late 1930s these 5"/51 (12.7 cm) SP guns and their cousins, the 5"/25 (12.7 cm) AA guns, were both replaced on new construction by the versatile 5"/38 (12.7 cm) Mark 12.

The British obtained three guns from Bethlehem Steel during World War I and employed them in the coastal defenses at Scapa Flow.  In 1918 a further 150 guns of an improved pattern were ordered to arm DAMS, but this order was cancelled at the end of the war.  These guns were designated as 5"/51 (12.7 cm) BL Mark VI and VII, respectively.  During World War II, 22 Mark 8 Mod 7 guns were supplied with the ten US Coast Guard Cutters transferred to Britain as a part of Lend-Lease.  Most of these guns were later replaced with British 4"/45 (10.2 cm) QF Mark V and other British AA weapons.  Some of the 5"/51 (12.7 cm) guns were then sent to New Zealand where they were used in coastal defenses.

The construction of the Mark 7 was similar to the previous 5"/50 (12.7 cm) Mark 6 and consisted of A tube, jacket, hoop, locking ring and screw box liner.  Some early Mark 7 guns were completed as case (semi-fixed) ammunition guns but were later converted to bag guns.  Used a side-swing Smith-Asbury, Welin breech block.  The Mark 8 gun used steel for some components and the chamber was slightly different, being constructed of tapered liner, A tube and full length jacket with a hoop and locking ring.  Used a breech bush and a liner locking bush with an Asbury Welin breech mechanism.  The Mark 9 was intended for submarines and was similar to the Mark 8, but had a different screw box liner, breech and chamber to allow the use of semi-fixed ammunition.  Mark 14 was a relined Mark 8 and Mark 15 was the Mark 14 with an enlarged chamber and a chromium plated bore.

The data that follows is specifically for the Mark 15 version unless otherwise noted.
WNUS_5-51_mk7_transport_pic.jpg

5"/51 (12.7 cm) on unidentified Navy Transport about 1942
U.S. Naval Historical Center Photograph # NH 80-G-K-11398
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Click here for additional pictures
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Gun Characteristics
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Designation 5"/51 (12.7 cm) Marks 7, 8, 9, 14 and 15
Ship Class Used On
(see Note)		 Battleship classes:  Florida (B-30), Wyoming (B-32), New York (B-34), Nevada (B-36), Pennsylvania (B-38), New Mexico (B-40), Tennessee (BB-43) and Colorado (BB-45)

Carrier classes:  Langley (CV-1), Long Island (AVG-1), Bogue (CVE-9), Sangamon (CVE-26) and Charger (CVE-30)

Destroyers:  Hatfield (D-231), Brooks (D-232), Gilmer (D-233), Fox (D-234) and Kane (D-235)

Submarines:  Barracuda (SS-163), Bonita (SS-164) and "T" (SS-198) class

Plus various Coast Guard cutters, auxiliaries and armed merchant ships
Date Of Design About 1910
Date In Service 1911
Gun Weight Mark 8 and Mark 15:  5.05 tons (5.13 mt)
Mark 9:  5.08 tons (5.16 mt)
Gun Length oa 261.25 in (6.636 m)
Bore Length 255 in (6.477 m)
Rifling Length Most guns:  212.1 in (5.387 m)
Mark 9:  214.1 in (5.438 m)
Grooves N/A
Lands N/A
Twist Mark 7 Mods 3 and 4:  Increasing RH 0 to 1 in 25 at the muzzle
Mark 7 Mod 2:  Uniform RH 1 in 25
Mark 8 Mods 0 - 1:  Increasing RH 0 to 1 in 25 at the muzzle
Mark 8 Mods 2 - 10:  Increasing RH 0 to 1 in 35 at the muzzle
Mark 9:  Uniform RH 1 in 30
Marks 14 and 15:  Uniform RH 1 in 35
Chamber Volume 1,202 in3 (19.7 dm3)
Rate Of Fire 8 - 9 rounds per minute
Note:  All destroyers of the Clemson (D-186) class had strengthened gun foundations which allowed them to mount heavier weapons than the standard single 4"/50 (10.2 cm) gun mounting.  However, only the five destroyers listed above plus three others that had twin 4"/50 (10.2 cm) mountings actually carried heavier weapons.
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Ammunition
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Type All except Mark 9:  Bag
Mark 9:  Separate
Projectile Types and Weights
(see Notes 1 and 2)		 AP - 50 lbs. (22.7 kg)
Common Mark 15 Mods 1 through 14 - 50 lbs. (22.7 kg)
HC Mark 39 Mods 1 and 2 - 50.0 lbs. (22.7 kg)
AAC Mark 35 Mods 1 through 12 - 55.18 lbs. (25.03 kg)
VT AA Mark 35 Mods 2 and 4 - 55.18 lbs. (25.03 kg)
Illum Mark 25 Mod 2 - 54.5 lbs. (24.7 kg)
Bursting Charge AP - 1.7 lbs. (0.77 kg) Explosive D
Common Mark 15 Mods 1 through 14 - 1.73 lbs. (0.78 kg) Black Powder and TNT
HC Mark 39 Mods 1 and 2 - 3.65 lbs. (1.66 kg) Explosive D
AAC Mark 35 Mods 1 through 12 - 7.25 lbs. (3.29 kg) Explosive D, Composition A
VT AA Mark 35 Mods 2 and 4 - 7.25 lbs. (3.29 kg) Explosive D, Composition A
Projectile Length Common Mark 15 Mods 12 and 14 - 17.0 in (43.2 cm)
Mark 39 Mods 1 and 2 - 17.0 in (43.2 cm)
Mark 35 - 20.7 in (52.6 cm)
Illum Mark 25 - 19.975 in (50.7 cm)
Cartridge Case Type, Size and Empty Weight
(Mark 9 gun only)		 Mark 3 - Brass, 127 x 839 mm, 27.38 lbs. (12.4 kg)
Propellant Charge
(see Notes 5 and 6)		 World War I
   24.5 lbs. (11.1 kg) SPD

World War II
   Full Charge - 25.0 lbs. (11.3 kg) SPD or SPDN
   Full Charge for AAC and AAVT only - 22.0 lbs. (10.0 kg) SPD or SPDN
   Full Flashless Charge - 26.0 lbs. (11.8 kg) SPDF
   Reduced Charge - 15.5 lbs. (7.0 kg) SPD or SPDN
   Reduced Flashless Charge - 15.5 lbs. (7.0 kg) SPDF
Muzzle Velocity Full Charge - New Gun
   All except AAC - 3,150 fps (960 mps)
   AAC and AAVT - 2,600 fps (792 mps)

Reduced Charge - New Gun
   2,300 fps (701 mps)
Working Pressure 17 tons/in2 (2,680 kg/cm2)
Approximate Barrel Life Mark 15:  900 rounds
Others:  About 700 rounds
Ammunition stowage per gun
(see Note 7)		 Delaware:  240 rounds
New York:  230 rounds
Pennsylvania:  230 rounds
Others:  N/A
Notes:

1) The AAC Mark 35 and Mark 36 projectile bodies could be used with Point Detonating (PD), Mechanical Time (MT) or with proximity (VT) fuzes.  When used with PD fuzes, they were considered to be HC rounds.  As the VT fuze was larger than the other ones, only certain projectile Mods could use it.

2) AAC rounds used both nose and base fuzes.  The base fuze was an instantaneous contact type while the nose fuze was a Mechanical Time type.  A blind plug was used in place of the base fuze for those projectiles using VT nose fuzes.

2) 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.

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

5) Semi-fixed and Bag charges used the same weight of propellant in most cases.  Reduced charges were used only for bag guns.

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

7) The New Mexico class (BB-40) had 24 ready rounds per gun.
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Range
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Elevation
With 50 lbs. (22.7 kg) AP
MV = 3,150 fps (960 mps)
Striking Velocity
Angle of Fall
0.3 degrees
1,000 yards (910 m)
2,846 fps (867 mps)
0.3
0.6 degrees
2,000 yards (1,830 m)
2,568 fps (782 mps)
0.6
1.0 degrees
3,000 yards (2,740 m)
2,308 fps (703 mps)
1.3
1.5 degrees
4,000 yards (3,660 m)
2,068 fps (630 mps)
2.0
2.0 degrees
5,000 yards (4,570 m)
1,848 fps (563 mps)
2.9
2.6 degrees
6,000 yards (5,490 m)
1,649 fps (503 mps)
4.1
4.2 degrees
8,000 yards (7,320 m)
1,319 fps (402 mps)
7.6
6.4 degrees
10,000 yards (9,140 m)
1,107 fps (337 mps)
12.7
9.3 degrees
12,000 yards (10,970 m)
1,013 fps (309 mps)
19.5
12.9 degrees
14,000 yards (12,800 m)
976 fps (297 mps)
27.0
17.3 degrees
16,000 yards (14,630 m)
969 fps (295 mps)
34.7
22.5 degrees
18,000 yards (16,460 m)
982 fps (299 mps)
42.2
25.0 degrees
18,800 yards (17,190 m)
994 fps (303 mps)
45.1
Notes:

1) This table reflects performance in the late 1920s and early 1930s.

2) Time of flight for MV = 3,150 fps (960 mps)
   1,000 yards (910 m):  1.0 seconds
   5,000 yards (4,570 m):  6.2 seconds
   10,000 yards (9,140 m):   17.0 seconds
   16,000 yards (14,630 m):  36.3 seconds
   18,800 yards (17,190 m):  47.8 seconds
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Elevation With 50 lbs. (22.7 kg) AP Shell
Range @ 15 degrees 14,050 yards (12,850 m)
Range @ 20 degrees 15,850 yards (14,490 m)
Range @ 45 degrees 20,142 yards (18,420 m)
Note:  This table reflects performance during World War II.
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Armor Penetration with 50 lbs. (22.7 kg) AP Shell
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Range
Side Armor
Deck Armor
3,200 yards (2,930 m)
4.0" (102 mm)
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5,200 yards (4,750 m)
3.0" (76 mm)
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8,000 yards (7,320 m)
2.0" (51 mm)
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19,600 yards (17,920 m)
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1.0" (25 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 "Dry" Single Mountings:  P13 and P15

Battleships:  Florida (16), Wyoming (21), New York (21), Nevada (21), Pennsylvania (22), New Mexico (14), Tennessee (14) and Colorado (12)

Carriers:  Langley (4), Long Island (1), Bogue (2), Sangamon (2) and Charger (1)

Destroyers:  Hatfield (3)

Coast Guard Cutters:  Lake Class (1)
 

"Wet" Single Mountings:  Mark 18

Submarines:  Barracuda (1), Bonita (1) and "T" (1)
Weight  P mountings:  10.0 to 11.9 tons (10.2 to 12.1 mt)

Mark 18:  10.7 tons (10.9 mt)
Elevation P13 Early Versions:  -10 / +15 degrees

P13 Later Versions:  -10 / +20 degrees

P15:  -15 / +20 degrees

Mark 18:  -8.5 / +25 degrees
Elevation Rate Manual operation, only
Train about +150 / -150 degrees
Train Rate Manual operation, only
Gun recoil N/A
Loading Angle Any
Notes:

1) All battleships had the later versions of the P13 mounting by the start of World War II.

2) Battleships carried up to twenty-two 5"/51 (12.7 cm) guns as commissioned, although many of these were removed during World War I in order to free up guns to arm Auxiliary vessels.  The forward and aft hull casemate guns were the first to go, as these tended to wash out in heavy seas and were thought to endanger the safety of the ship.  The Captain of the Pennsylvania (B-38) expressed the view that the British battleship Audacious - lost due to mine damage - would not have sunk had she not flooded through her after gun ports.  During the war, the Wyoming (B-32) and New York (B-34) classes lost five guns, the Nevada class (B-36) lost nine guns and the Pennsylvania class (B-38) lost eight guns.  Battleships serving with the British Grand Fleet retained their secondary batteries until after the war, although the Captain of Texas (B-35) reported in May 1919 that he considered the hull mounted guns to be of little use and that their crews crowded the ship.  The Tennessee (BB-43) class were the first US battleships to have all secondary guns mounted on or above the weather deck as completed.  By 1921 the approved ultimate secondary batteries for the "Standards" was twelve 5"/51 (12.7 cm) and eight 3"/50 (7.62 cm) AA guns and the Colorado class (BB-45) was completed with this armament.  Some battleships had the number of these guns reduced during the 1920s in order to mount 5"/25 (12.7 cm) AA guns.  During the 1930s rebuilds of the battle line, "Standard" battleships with hull mounted guns had them removed and resited in the superstructure.  By 1941, Arkansas (BB-33), New York (BB-34) and Texas (BB-35) carried sixteen 5"/51 (12.7 cm) guns, Nevada (BB-36) through California (BB-44) carried twelve guns and the Colorado class (BB-45) carried ten guns.  During the war, Nevada (BB-36), Pennsylvania (BB-38), Tennessee (BB-43), California (BB-44), Maryland (BB-46) and West Virginia (BB-48) replaced their mixed batteries of 5"/51 (12.7 cm) SP and 5"/25 (12.7 cm) AA guns with a uniform battery of sixteen (8x2) 5"/38 (12.7 cm) DP guns.  New Mexico (BB-40) had all her 5"/51 (12.7 cm) guns removed in late 1942 and her light AA armament greatly increased.  Mississippi (BB-41) had all of her 5"/51 (12.7 cm) guns removed in 1945 in order to allow a total battery of sixteen 5"/25 (12.7 cm) AA guns.  Idaho (BB-42) replaced her mixed 5" (12.7 cm) batteries in late 1944 with ten 5"/38 (12.7 cm) DP guns in single mounts.  Removed guns were reused during World War II on Auxiliaries and in coastal batteries.

3) During World War II, Escort Carriers of the Bogue class (CVE-9) traded their two 5"/51 (12.7 cm) guns for two 5"/38 guns.

4) Most deck mounts on all ship types did not have gun shields, leaving their crews exposed to shrapnel.

5) A twin mounting designated as the Mark 14 was was approved in 1919 and a prototype was under construction later that year.  These were to be used to rearm the the older dreadnought battleships of the Florida (B-30) through New York (B-34) classes.  However, trouble with the prototype led to the project being abandoned in November 1919 and by December removed guns were being reinstalled on these ships.
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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
"US Battleships:  An Illustrated Design History" and "US Naval Weapons" both by Norman Friedman
"U.S. Warships of World War II" by Paul H. Silverstone
"Battleships of World War Two" by M.J. Whitley
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"Range and Ballistic Tables 1935" by U.S. Department of Ordnance and Gunnery
"U.S. Explosive Ordnance:  Ordnance Pamphlet 1664 - May 1947" by Department of the Navy
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"Ordnance Pamphlet 127:  United States Naval Guns, Their Marks and Modifications April 1942" at Gene Slover's US Navy Pages
Page History

09 February 2008 - Benchmark
25 January 2009 - Added information on British guns, added construction information on the Mark 8
28 September 2009 - Added information concerning use on escort carriers
30 November 2009 - Adjusted description of nose fuzes
12 February 2012 - Updated to latest template
23 February 2013 - Added notes regarding changes to battleship secondaries