Britain
8"/50 (20.3 cm) Mark VIII
Updated 18 February 2009
This weapon was designed for Britain's Treaty Cruisers of the 1920s.  Similar to other cruisers of that era, the mountings for these weapons were given a high maximum elevation in order to provide an anti-aircraft capability.  However, the training and elevation gear was inefficient and both the elevation and training rates were too slow to allow these mountings to be useful in that role.

The complex nature of the early versions of these mountings, the Mark I and Mark I*, gave trouble for a number of years.  Considerable attention was paid to these faults, especially in 1927 and 1928, before these ships were accepted into service.  After the initial trials, the training and elevation rates were reduced prior to commissioning and reduced still further during the 1930s in an effort to improve the operational performance of the turrets.

On 26 July 1929, one of these guns on HMS Devonshire suffered a catastrophic breech failure at the first salvo during a practice firing.  One shell and a number of cordite bags were ignited, blowing off the roof of "X" turret and killing one officer and seventeen crewmen.

Most of the problems seem to have been satisfactorily resolved prior to the start of World War II, but HMS London reported as late as June 1938 that "one would wish that the 8in mountings and torpedoes would behave as they should.  The prolonged firing of 20 rounds per gun from London was a disappointment on the material side."

The later Mark II mountings appear to have been much more reliable, with the first gun trials for HMS York in February 1930 being so successful that they took only four hours to complete.  As a weight saving measure, the Mark II* version of this mounting, used only on HMS Exeter, had a significantly reduced maximum elevation.

The original design was A tube, wire, B tube, overlapping jacket, breech ring and breech-bush and these guns were designated as Mark VIII* upon completion.  Owing to troubles with the A tube forging, an inner A tube was added to half of the wire wound guns.  After relining with a tapered inner A tube, guns were then designated as Mark VIII.  Two prototypes and the last 26 guns built did not use wire and were designated as Mark VIII**.  All guns used a Welin breech-block with hydraulic or hand worked Asbury mechanism and were interchangeable with each other.  A total of 168 guns were produced, including the two prototypes built without wire.

Six Mark VIII** guns were used as coastal artillery in the Dover - Folkestone area during World War II.  These were in single mountings capable of +70 degree elevation.
WNBR_8-50_mk8_Australia_pic.jpg

HMAS Australia on a visit to New York in 1932
Note the large gunports of these Mark I turrets, which allowed +70 degree elevations
U.S. Naval Historical Center Photograph # NH 52682
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Click here for additional pictures
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Gun Characteristics
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Designation 8"/50 (20.3 cm) Mark VIII
Ship Class Used On Kent, London, Norfolk and York classes
Australia class (modified Kent)
Date Of Design 1923
Date In Service 1927
Gun Weight Mark VIII and VIII*:  38,528 lbs. (17,476 kg)
Mark VIII**:  38,640 lbs. (17,527 kg)
Gun Length oa 413.1 in (10.493 m)
Bore Length 400.0 in (10.160 m)
Rifling Length 346.3 in (8.796 m)
Grooves (48) 0.055 in deep x 0.376 (1.40 x 9.55 mm)
Lands 0.1476 in (3.749 mm)
Twist Uniform RH 1 in 30
Chamber Volume 3,646 in3 (59.75  dm3)
Rate Of Fire
(see Note)		 3 - 6 rounds per minute
Note:  The original Naval Staff requirement for these weapons was 12 rounds per minute, an impossibly high figure for the time.  The requirement was ultimately reduced to six rounds per minute.  However, "British Cruisers of World War Two" states that this rate was never reached during wartime service and that the maximum sustained ROF in action was actually 3 to 4 rounds per minute.  During trials, HMS Kent did achieve a ROF of 5 rounds per minute for a brief time.
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Ammunition
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Type Bag
Projectile Types and Weights SAPC - 256 lbs. (116.1 kg)
HE - 256 lbs. (116.1 kg)
Bursting Charge SAPC - 11.5 lbs. (5.2 kg)
HE - about 23 lbs. (10 kg)
Projectile Length SAPC - 36 in (91.4 cm)
HE - N/A
Propellant Charge
(see Note 3)		 66.0 lbs. (29.94 kg) SC 205
Muzzle Velocity 2,805 fps (855 mps)
Working Pressure 20.5 tons/in2 (3,230 kg/cm2)
Approximate Barrel Life 550 rounds
Magazine capacity per gun Country classes:  125 - 150 rounds
York class:  172.5 rounds
Notes:

1) Propellant was in halves.

2) Outfits were mainly SAPC with 20 rounds of HE per gun.

3) The original muzzle velocity was 2,900 fps (884 mps) with a 72.25 lbs. (32.77 kg) SC charge, but this was derated to the figure given above in order to reduce dispersion and increase liner life.
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Range
Muzzle Velocity of 2,725 fps (831 mps)
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Elevation With 256 lbs. (116.1) SAPC Shell
Range @  2.1 degrees 5,000 yards (4,570 m)
Range @ 5.2 degrees 10,000 yards (9,140 m)
Range @ 9.8 degrees 15,000 yards (13,720 m)
Range @ 16.5 degrees 20,000 yards (18,290 m)
Range @ 26.7 degrees 25,000 yards (22,860 m)
Range @ 41.5 degrees 29,000 yards (26,520 m)
Range @ 45 degrees 30,650 yards (28,030 m)
Note:  Time of flight for SAPC Shell with MV = 2,725 fps (830.5 mps)
   5,000 yards (4,570 m):  6.2 seconds
   10,000 yards (9,140 m): 14.1 seconds
   15,000 yards (13,720 m):  24.7 seconds
   20,000 yards (18,290 m):  38.4 seconds
   25,000 yards (22,860 m):  55.9 seconds
   29,000 yards (26,520 m):  78.6 seconds
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Mount / Turret Data
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Designation Twin Mounts
   Kent (4) and Australia (4):  Mark I
   London (4):  Mark I*
   Dorsetshire (4) and York (3):  Mark II
   Exeter (3):  Mark II*
Weight
(see Note 2)		 Original Estimate
   Mark I:   155 tons (157 mt)
   Mark I*:  159.5 tons (162 mt)
   Mark II:   168.8 tons (172 mt)
   Mark II*:  N/A

As Completed
   Mark I:   205 tons (226 mt)
   Mark I*:  210 tons (231 mt)
   Mark II:  220.3 tons (242 mt)
   Mark II*:  N/A
Elevation Mark I, I* and II:  -3 / +70 degrees 

Mark II*:  -3 / +50 degrees
Elevation Rate As originally designed:  10 degrees per second. 

Final design:  4 - 5.5 degrees per second
Train about +150 / -150 degrees
Train Rate
(see Note 4)		 As originally designed:  8 degrees per second

Final design:  5 - 6 degrees per second
Gun recoil 24 in (61 cm)
Loading Angle Mark I and I*:  10 degrees

Mark II and II*:  6 degrees
Notes:

1) In the Mark I mountings, the shell handling room was unprotected and was located above the cordite handling room, which was in a protected volume.  The Mark II mountings had the cordite and shell rooms combined in a single protected volume, which also had the effect of simplifying the ammunition supply to the hoists.

2) The estimated versus actual weights of these mountings show the difficulties involved during the design phase in correctly computing weight.  As these were Treaty-limited warships, these overruns for the main armament had to be compensated for by taking weight out of other areas, such as reducing the number of hull scantlings.  It was originally hoped that the Mark II mounting would be much lighter than the Mark I, but the reverse turned out to be the case.

3) These mountings used one hydraulic pump per mounting located on the revolving structure and driven by a 120 bhp electric motor.  There was also a hydraulic pump in "A" and "X" shell rooms to power the fittings used in the bow and stern shell rooms and shell handling rooms.  Mineral oil was used as the pressure medium to allow the use of lighter and lower cost steel in place of brass piping and to avoid corrosion in the pusher hoists, which were "most inaccessible."  Elevation was by a 13 bhp swashplate engine driving through gearing and worm toothed arcs on the underside of the cradle.

4) Training was by two 40 bhp swashplate engines of which only one was used at a time and which drove a worm gear.  These were capable of training at 8 degrees per second, but were limited to 6 degrees per second by other demands on the pump and to only 2 degrees per second during loading operations.

5) Australia, Devonshire and Sussex had "X" turret removed during the war as weight compensation for additional light AA, radar and other electronic equipment.

6) The gun axes were 84 in (213 cm) apart on all versions.
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Data from
"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 8" article in "Warship Volume VII" both by John Campbell
"The Price of Disobedience:  The Battle of the River Plate Reconsidered" by Eric Grove
"British Cruisers of World War Two" by Alan Raven and John Roberts
"Cruisers of World War Two" by M.J. Whitley
Page History

01 August 2008 - Benchmark
18 February 2009 - Added additional construction details