Britain
6"/50 (15.2 cm) BL Mark XXII
Updated 05 January 2014

A more powerful weapon than the previous 6" (15.2 cm) Mark XII, this gun was originally designed for the never-built "G3" battlecruisers.  When those ships were canceled as a result of the Washington Naval Limitation Treaty, the guns and mountings were then used on the Nelson class battleships.  These were the first British battleships to carry their secondary armament in turrets rather than in broadside casemates.

Like many British medium-caliber mountings of the 1920s, these guns had a high maximum elevation so that they could engage aircraft, but this was of secondary importance to their use in the anti-ship role.  In reality, the training and elevation speeds of the mountings were too slow for the AA role. 

The arrangement on the Nelson class had a major disadvantage in that all turrets and their working spaces were grouped tightly together.  As the turrets and working spaces were only lightly protected by 1" (25 mm) HT plating, this meant that a single shell could have disabled all guns on one side.

The Mark XXII* was constructed of A tube, taper wound wire, full-length jacket, breech ring and breech bush screwed into the A tube.  Used a hand-operated Welin breech block.  When this gun was relined with a tapered inner A tube having three locating shoulders, it became the Mark XXII.  The later Mark XXII** was built without wire and used an inner A tube.  A total of 40 guns were built, including two experimental guns and six Mark XXII**.

WNBR_6-50_mk22_pic.jpg

HMS Nelson
Note the small rangefinder on the right and the 4.7"/40 (12 cm) AA gun on the left

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P3 Turret on HMS Nelson in 1932
RAF Museum Photograph

WNBR_6-50_mk22_Rodney_pic.jpg

Port 6"/50 (15.2 cm) turrets on HMS Rodney in 1940
IWM photograph A 95

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Interior of a Mark XVIII turret on HMS Rodney
Note the ready ammunition clipped to the walls and the power rammer, an unusual feature for British 6" (15.2 cm) guns.
16 men worked and slept in the turret during the war when the ship was at sea.  Note the communication number (wearing headphones) remaining awake while his fellows slept.
IWM photograph A 2134

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Gun Characteristics
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Designation 6"/50 (15.2 cm) BL Mark XXII
Ship Class Used On Nelson Class
Date Of Design about 1921
Date In Service 1926
Gun Weight Mark XXII and Mark XXII*
   Without Breech:  19,824 lbs. (8,992 kg)
   Weight of Breech:  364 lbs. (165.1 kg)

Mark XXII**
   Weight with Breech:  20,212 lbs. (9,168 kg)

Gun Length oa 309.7 in (7.866 m)
Bore Length 300 in (7.620 m)
Rifling Length 255.6 in (6.491 m)
Grooves (36) 0.046 in deep x 0.3759 (1.17 x 9.548 mm)
Lands 0.1477 in (3.752 mm)
Twist Uniform RH 1 in 30
Chamber Volume 1,750 in3 (28.7  dm3)
Rate Of Fire
(see Note)
5 rounds per minute
Note:  The original design requirement was for a rate of fire of 7 to 8 rounds per minute.  On trials, the best rate achieved was 4 rounds per minute.  During her battle with Bismarck, Rodney fired 150 salvos from her starboard battery at an average of 5 salvos per minute and 98 salvos from her port battery at an average of 3.9 salvos per minute.  During the first 9 minutes at close range she achieved 5.9 rounds per minute and an output of nearly 100%.  In all, Rodney fired 716 rounds of 6" (15.2 cm) CPBC during this action.
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Ammunition
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Type Bag
Projectile Types and Weights CPBC Mark XXVB - 100 lbs. (45.36 kg)
CPBC (1942) - 112 lbs. (50.8 kg)
HE - N/A
Bursting Charge N/A
Projectile Length N/A
Propellant Charge 31 lbs. (14.1 kg) SC 150
Muzzle Velocity 2,945 fps (898 mps)
Working Pressure 20 tons/in2 (3,150 kg/cm2)
Approximate Barrel Life 600 rounds
Ammunition stowage per gun Normal:  100 rounds
Maximum:  150 rounds
Notes:

1) The propellant was in a single bag.  Flashless does not seem to have been issued.

2) As of 1942, the same projectiles as used for the Mark XXIII were issued for these guns.

3) Maximum ammunition stowage consisted of 135 CPBC, 15 HE and 24 practice rounds per gun.  In addition, there were 72 smoke shells provided per ship.

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Range
At 2,900 fps (884 mps)
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Elevation
With 100 lbs. (45.36) CPBC Shell
Range @ 2.1 degrees
5,000 yards (4,570 m)
Range @ 5.6 degrees
10,000 yards (9,140 m)
Range @ 12.1 degrees
15,000 yards (13,720 m)
Range @ 22.9 degrees
20,000 yards (18,290 m)
Range @ 42.6 degrees
25,000 yards (22,860 m)
Range @ 45.0 degrees
25,800 yards (23,590 m)
Note:  Time of flight for CPBC Shell with MV = 2,900 fps (884 mps)
   5,000 yards (4,570 m):  6.2 seconds
   10,000 yards (9,140 m): 15.2 seconds
   15,000 yards (13,720 m):  28.6 seconds
   20,000 yards (18,290 m):  46.1 seconds
   25,000 yards (22,860 m):  74.9 seconds
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Mount / Turret Data
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Designation Twin Mounts
   Nelson (6):  Mark XVIII
Weight  168,000 lbs. (76,204 kg)
Elevation -5 / +60 degrees
Elevation Rate 8 degrees per second
Train about +100 / -100 degrees
Train Rate about 5 degrees per second
Gun recoil 16.5 in (42 cm)
Loading Angle +5 degrees
Notes: 

1) Telescopic power rammers were used, but the firing cycle was much slower than in earlier mountings.

2) These mountings had very through flash precautions, which may have contributed to the slower ROF.  However, the use of turrets meant that much of the ammunition supply could be automated, thus reducing crew fatigue, and they had better arcs of fire both in both the horizontal and vertical planes.  As they were mounted on the weather deck, this also meant that they were drier and could function even in heavy seas that would wash out the broadside mounts of earlier designs.

3) Turrets were powered by a 60 bhp electric motor driving a hydraulic pump.  A single swashplate engine was used for training while elevation was apparently by a swashplate engine turning a worm gear.

4) The ammunition supply for these mountings was somewhat clumsy.  There was a lower magazine with one handling room.  Two hoists supplied the working spaces of P1 and S1 turrets (the forward ones on each side), while an upper magazine with two handling rooms and four hoists supplied the working spaces of the other four turrets.  The shell room was above the lower magazine and was equipped with six hoists.  The charge hoists were endless chains while the shell hoists were of a pusher type, all of which were electrically powered.  The upper hoists from the handling rooms to the turrets were hydraulically powered.  There was one charge and one shell hoist per gun.  Charges were stored in Clarkson's cases and went up the hoist in them and not removed until just before loading.  The cases were returned to the working chamber via a tube and then to the magazines by the down side of the lower hoists and through flashtight scuttles.

5) The following comments are from the report by Capt. Thomas Hugh Binney (RN) to the Admiralty upon finishing his tour of command of Nelson in 1930:

In the case of the secondary armament, although the rate of fire is rather low, the increased range at which fire can be opened, and the absence of loss of output due to fatigue, combined with excellent ammunition supply arrangements, will be a very pronounced factor in war.

In view of the modern tendency of construction for 'all or nothing' armour protection leaving controls and secondary batteries unprotected, the possibility for using the secondary battery for 'harassing fire' at the main armoured target when the range has been found assumes greater importance, and in Nelson the secondary armament can do this efficiently without loss of anti-torpedo boat efficiency.

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Data from
"British Battleships 1919 - 1945:  New Revised Edition" by R.A. Burt
"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 13" article in "Warship Volume VIII" both by John Campbell
"Battleship Nelson:  The Story of HMS Nelson" by Ronald Careless
"British Battleships of World War Two" by Alan Raven and John Roberts
"The Final Action:  The Sinking of Bismarck, 27 May 1941" article by John Roberts in "Warship Volume VII"
Page History

07 January 2007 - Benchmark
11 February 2012 - Updated to latest template
03 June 2012 - Added mounting notes, added comments by Capt. Binney
05 January 2014 - Added photographs of turrets on HMS Rodney