British
4.7"/50 (12 cm) QF Mark XI
Updated 05 March 2007
By 1938, the Admiralty recognized that British destroyers compared badly with their USA and Japanese counterparts, as they were lacking DP main guns and weather-proof mounts.  The 4.7"/50 (12 cm) Mark XI guns and Mark XX twin mounting were intended to correct these deficiencies.  These guns fired a heavier shell of more modern design and their mountings allowed higher elevations than did most other British guns of this caliber.  However, their training rate and manually operated elevation gear limited their usefulness in the AA role and for that reason many of these destroyers had the after torpedo mounting replaced during World War II with a single 4" (10.2 cm) AA gun.

In my opinion, this was Britain's best destroyer gun of World War II for surface action, although its low maximum elevation and speeds made it only marginally useful for anti-aircraft defense.  Unfortunately, the cost of these destroyers was so much greater than the previous designs that only a few were built and newer destroyers reverted to the cheaper SP gun.

The guns were in separate sleeves, allowing them to be elevated individually.  The mountings had hydraulic training, ramming and shell hoists and were quite complicated, which resulted in long production delays and caused four of the L class destroyers to be completed with four twin 4" (10.2 cm) Mark XIX mounts in place of the 4.7" (12 cm) mounts.

In 1958 four "M" class destroyers were sold to Turkey and were extensively refitted.  One of the modifications was to add power elevation, thus correcting one of the major deficiencies of this mounting.

Constructed of autofretted loose barrel, jacket, removable breech ring and sealing collar.  Used a manually operated breech mechanism with semi-automatic breech opening.  A total of 87 guns were manufactured.

Actual bore diameter of all British 4.7" guns was 4.724" (12 cm).
WNBR_47-50_mk11_Laforey_pic.jpg

HMS Laforey
Click on this picture for a larger image
Note the amidships quad 2-pdr and the 4" (10.2 cm) HA gun directly behind it
IWM Photograph
WNBR_47-50_mk11_Turret_pic.jpg

4.7"/50 (12 cm) Mark XI in Mark XX mounting leaving the gun shop
MoD photograph
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Detailed Sketch of 4.7 in/50 (12 cm) Mark XX Mounting
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Images at The Vickers Photographic Archive

See Mark XX Mounting

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Gun Characteristics
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Designation 4.7"/50 (12 cm) QF Mark XI
Ship Class Used On L and M Classes
Date Of Design about 1938
Date In Service 1940
Gun Weight 3.351 tons (3,405 kg)
Gun Length oa 247.7 in (6.292 m)
Bore Length 236.2 in (6.000 m)
Rifling Length 204.9 in (5.204 m)
Grooves (38) 0.0365 in deep x 0.270 (0.927 x 6.86 mm)
Lands 0.1205 in (3.061 mm)
Twist Uniform RH 1 in 30
Chamber Volume 670 in3 (10.98 dm3)
Rate Of Fire 6 - 10 rounds per minute
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Ammunition
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Type Separate
Projectile Types and Weights HE - 62 lbs. (28.12 kg)
SAP - 62 lbs. (28.12 kg)
Bursting Charge N/A
Projectile Length N/A
Propellant Charge 12.81 lbs. SC or 15.38 lbs. NF/S (5.81 or 7.0 kg)
Cartridge - 32.25 lbs. (14.63 kg)
Muzzle Velocity 2,538 fps (774 mps)
Working Pressure 20.5 tons/in2 (3,230 kg/cm2)
Approximate Barrel Life 800 rounds
Ammunition stowage per gun N/A
Notes:

1) This was the only weapon of this caliber to fire projectiles of modern design with 5/10crh heads and heavier weight.
2) Outfits included SAP, HE and star shells.  Sixty special anti-submarine HE shells with RDX/TNT fillers were supplied to each ship by 1945 and the star shell allotment was 150 - 200 rounds per ship.
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Range
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Elevation With 62 lbs. (28.12 kg) HE Shell
Range @ 45 degrees 21,240 yards (19,420 m)
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Armor Penetration with 62 lbs. (28.12 kg) SAP Shell
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Range
NC Armor
Deck Armor
11,500 yards (10,500 m)
2.5" (76 mm)
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Note:  Data from "British Battleships of World War Two."  Assumes a perpendicular impact.
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Mount / Turret Data
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Designation Twin Mounting
   L and M classes (3):  CP Mark XX
Weight  Gunhouse including guns:  84,217 lbs. (38,200 kg)
Including mount base and hoists:  128,089 lbs. (58,100 kg)
Elevation -10 / +50 degrees
Elevation Rate
(see Note 2)		 Manually operated, only
Train about +150 / -150 degrees
Train Rate 10 degrees per second
Gun recoil 26.5 in (67.3 cm)
Notes:

1) Intended to save costs, an unusual feature of this mounting was that only the gunhouse rotated, the ammunition supply hoists did not rotate and were part of the fixed structure.  This design necessitated that the ammunition and powder hoists needed to come up at the center of rotation, which explains why the guns are so widely separated in this mounting.  Since the hoists did not rotate with the mounting, large angles of train caused difficulties with transferring ammunition to the guns and thus slowed down the ROF.  "Destroyer Weapons of World War 2" notes that a true turret mounting including a rotating stalk would have almost certainly been rejected by the Exchequer for cost reasons.  However, given the actual cost growth experienced during design and construction, one must wonder if the final cost of such a true turret mounting would have been much if any different.  It almost certainly would have meant a smaller gunhouse.

2) The widely separated gun barrels meant that dual elevation mechanisms were needed.  As built, these were manually operated, as the extra weight involved ruled out power drives.  Power elevation was fitted to the four "M" class destroyers sold to Turkey in 1958.  I lack the elevation rate for these modified mountings.

3) The mounings were powered by a 45 bhp (peak 102 bhp) electric motor and oil hydraulic pump on the fixed structure.  Training was by a single hydraulic motor with two worm and pinion drives.  Run out was powered by compressed air.  Each gun had its own shell hoist and charge hoist.

4) The gun axes were 96 in (244 cm) apart.  How astonishingly wide this is may be appreciated by noting that the gun axes for the 15"/42 (38.1 cm) Mark I twin mounting used on Capital ships were actually narrower by 6 inches (15.2 cm).  The gun axes for the concurrent 4.7"/45 (12 cm) Mark CPXIX twin mounting used on other British destroyers were considerably narrower at 38 in (96.5 cm).
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Data from
"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 15" article in "Warship Volume IX" both by John Campbell
"Destroyer Weapons of World War 2" by Peter Hodges and Norman Friedman
"Destroyers at War" by Gregory Haines
"Okrety Rzeczpospolitej Polskiej 1920-1946" ("Warships of Republic of Poland 1920-1946") by Stanislaw M. Piaskowski
"Destroyers of World War Two" by M.J. Whitley
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Special help from Andrzej Sluzek