BL 8-inch Mk VIII naval gun
The 50 calibre BL 8 inch gun Mark VIII was the main battery gun used on the Royal Navy's County-class heavy cruisers, in compliance with the Washington Naval Treaty of 1922. This treaty allowed ships of not more than 10,000 tons standard displacement and with guns no larger than 8 inches (203 mm) to be excluded from total tonnage limitations on a nation's capital ships. The 10,000 ton limit was a major factor in design decisions such as turrets and gun mountings. A similar gun formed the main battery of Spanish Canarias-class cruisers. In 1930, the Royal Navy adopted the BL 6 inch Mk XXIII naval gun as the standard cruiser main battery in preference to this 8-inch gun.
|Ordnance BL 8 inch gun Mk VIII|
Forward 8-inch turrets aboard HMAS Canberra
Coast defence gun
|Place of origin||United Kingdom|
|In service||1927 – 1954|
|Used by||Royal Navy |
Royal Australian Navy
|Wars||Second World War |
Spanish Civil War
|Barrel length||400 inches/10 meters(50 calibres)|
|Shell||256 pounds (116 kg)|
|Calibre||8-inch (203 mm)|
|Muzzle velocity||2805 feet per second (855 m/s)|
|Maximum firing range||28 kilometres (17 mi)|
These built-up guns consisted of a wire-wound tube encased within a second tube and jacket with a Welin breech block and hydraulic or hand-operated Asbury mechanism. Two cloth bags each containing 15 kg (33 lb) of cordite were used to fire a 116 kg (256 lb) projectile. Mark I turrets allowed gun elevation to 70 degrees to fire high-explosive shells against aircraft. Hydraulic pumps proved incapable of providing sufficient train and elevation speed to follow contemporary aircraft; so simplified Mark II turrets with a maximum elevation of 50 degrees were installed in the Norfolk subgroup ships Dorsetshire and Norfolk and the York-class cruisers York and Exeter. Each gun could fire approximately five rounds per minute. Useful life expectancy was 550 effective full charges (EFC) per barrel.
The following ships mounted Mk VIII guns in 188-tonne twin turrets. The standard main battery was four turrets, but Exeter and York carried only three to reduce weight and formed the separate York class.
- County-class heavy cruisers : 14 ships
- Canarias-class heavy cruisers : 2 ships
- York-class heavy cruisers : 2 ships
Coast defence guns
- A gun from HMAS Australia outside the Australian War Memorial, Canberra
- Mark VIII = Mark 8. Britain used Roman numerals to denote Marks (models) of ordnance until after World War II. Hence this was the eighth model of BL 8-inch naval gun.
- A more accurate term is "Treaty Cruiser", as the term heavy cruiser was only formally defined at the time of the London Naval Treaty of 1930. However, all the 8-inch gun cruisers introduced as a result of the 1922 Washington Treaty were what became known as "heavy cruisers".
- Whitley 1995 pp.17,83&89
- Campbell 1985 pp.31–33
- Campbell 1985 p.389
- Whitley 1995 pp.96–127
- Lenton & Colledge 1968 pp. 36–39
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