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.
HMAS Australia on a visit to New York in
|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.
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
|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.|
|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
(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
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.
|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
Kent (4) and Australia (4): Mark I
London (4): Mark I*
Dorsetshire (4) and York (3): Mark II
Exeter (3): Mark II*
(see Note 2)
Mark I: 155 tons (157 mt)
Mark I*: 159.5 tons (162 mt)
Mark II: 168.8 tons (172 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
Final design: 4 - 5.5 degrees per second
|Train||about +150 / -150 degrees|
(see Note 4)
|As originally designed: 8 degrees
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
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.
01 August 2008 - Benchmark
18 February 2009 - Added additional construction details