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.

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.

On 26 July 1929, HMS Devonshire suffered a misfire with the left gun in "X" turret. A crewman, unaware of the issue, opened the breech too soon and the inrush of oxygen set off the charges. One shell and a number of cordite bags were ignited, blowing off the turret roof and killing one officer and seventeen crewmen. Some evidence exists that the British added a "Salvo Latch" to these guns in order to prevent such mishaps in the future.

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.

• ^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.

• ^Australian cruisers ran out of British HE shells in 1942 and were unable to obtain more due to other priorities at the munitions factories. Experiments showed that USN 8in (20.3 cm) HC shells with reduced charges could be substituted and these were then used for shore bombardment missions for the rest of the war.
• ^Propellant was in halves.
• ^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.
• ^Outfits were mainly SAPC with 20 rounds of HE per gun.

• ^Magazines and shell rooms were on the same level. Charges were passed to the handling room through flashtight revolving scuttles and placed on waiting trays attached to the hoist trunk. This contained a cordite hoist for each gun and each hoist had two cages so that while one was being unloaded, the other cage was loading in the handling room. Charges were horizontal when lifted. In the shell rooms, shells were handled by powered overhead gear. At each side there was a transporter hoist which delivered shells to the shell ring in the shell handling room. The shell ring was hydraulically powered and ran on a roller path bolted to the deck of the shell handling room. It had 30 compartments, each handling one shell in a vertical position. Two hand-operated shell bogies which could be locked to one of the compartments to pick up a shell and then moved and locked to the hoist trunk to deliver the shell to the hoist. There was one shell hoist per gun. In the gunhouse, charges were rammed by hand from the hoist cage to the cordite compartment of the hollow rammer. The shell hoist deposited the projectiles in rear of the gun in a shell tilting tray. The hollow rammer pivoted from the cordite hoist to the breech and rammed the shell with the charges being rammed in the same stroke by a coaxial ram.
• ^Australia, Devonshire and Sussex had "X" turret removed during the war as weight compensation for additional light AA, radar and other electronic equipment.
• ^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.
• ^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.
• ^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.
• 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.
• The gun axes were 84 in (213 cm) apart on all versions.

The Vickers Photographic Archive
See photograph numbers 7119 and 7120

Australian War Memorial
Pictures of 8" (20.3 cm) guns being relined at Bendigo Ordnance Factory: 086425 and P00444.161
Additional pictures of British 8" (20.3 cm) naval guns in Australian service: HMAS 8 inch guns

"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 8" article in "Warship Volume VII" both by John Campbell
"As Luck Would Have It: The Reminiscences of an Australian Sailor" by Sir John Collins
"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
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From the Devon and Exeter Gazette of 31 July 1929: "OVER EAGERNESS PROBABLE CAUSE OF THE NAVAL DISASTER - An Admiralty communique last night attributes the accident on HMS Devonshire in the Eastern Mediterranean, to hangfire of a very short duration in one gun of an eight-inch turret. It was probably thought momentarily that the gun fired, and the operation of reloading was commenced. The breech was initially opened, and before the mistake could be rectified, the charge in the gun exploded. The force of the explosion also ignited the cordite charges waiting for the next round."
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"C.B. 1797 - Handbook for 8-inch B.L. Mark VIII* Gun on Twin Mark I Mounting" by Admiralty, S.W.1. Gunnery Branch, September 1928
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Special help from Chris Campbell and Neil Stirling

01 August 2008 - Benchmark
18 February 2009 - Added additional construction details
25 January 2010 - Recropped photograph of HMS York for better view
19 June 2012 - Added photograph of HMAS Shropshire
07 January 2013 - Added photograph of Australian cruiser
06 May 2014 - Added photograph of Exeter following repairs
01 December 2015 - Changed Vickers Photographic Archive links to point at Wayback Archive and updated links to Australian War Memorial
24 September 2018 - Converted to HTML 5 format, reorganized notes and added data to Range Table
19 February 2019 - Corrected typographical error
17 April 2021 - Corrected range table
19 February 2022 - Changed reason for HMS Devonshire explosion, added ammunition details and ammunition handling note
15 September 2023 - Added note regarding use of HC ammunition on Australian cruisers
22 March 2024 - Added sketches from C.B. 1797
03 August 2024 - Added to caption for SAPC projectile sketch