Military Wiki
Ordnance BL 12 inch gun Mk I - VII
HMS Conqueror Forecastle Guns Clipped300px.jpg
On HMS Conqueror
Type Naval gun
Coastal gun
Place of origin United Kingdom
Service history
In service 1882–1920
Used by Royal Navy
Production history
Variants Mks I - VII[note 1]
Weight Mk I : 47 tons barrel & breech
Mk II - V 45 tons[1]
Mk VI, VII : 46 tons
Barrel length Mk I & II : 301.7 inches (7.663 m) bore (25.14 calibres)
Mk III - VII 303 inches (7.696 m) bore (25.25 calibres)[2]

Shell 714 pounds (324 kg)[1]
Calibre 12-inch (304.8 mm)
Muzzle velocity 1,910 feet per second (582 m/s)[3]
Effective range 8,000 yards (7,300 m) at 9° 57'[4]

The BL 12 inch naval gun Mk I was a British rifled breech-loading naval gun of the early 1880s intended for the largest warships such as battleships and also coastal defence. It was Britain's first attempt to match the large guns being installed in rival European navies, particularly France, after Britain transitioned from rifled muzzle-loading guns to the modern rifled breech-loaders somewhat later than the European powers. Mks I - VII[note 1] all had a barrel of approximately 303 inches in length (25.25 calibres) and similar performance.

Naval service

Mk II was installed on battleships Colossus (1882) from 1882, Collingwood (1882) and the coastal service ironclad Conqueror (1881). Mk II guns failed in service and were quickly replaced by Mks III. IV and V, with many changes and improvements. The later marks were also mounted on Hero (1885), sistership of Conqueror, and on Edinburgh (1882), sister ship of Colossus.

Coast defence gun

Mks I, VI and VII were coast defence versions with trunnions for mounting on recoil slides. They were installed in forts in England at Spitbank Fort, No Man's Land Fort and Horse Sand Fort from 1884 onward and were in active service during World War I.[5]


See also


  1. 1.0 1.1 Mk I = Mark 1, Mk VII = Mark 7. Britain used Roman numerals to designate marks (i.e. models) of ordnance until after World War II. Hence this article describes the first seven models of British BL 12-inch guns


  1. 1.0 1.1 Text Book of Gunnery, 1887. Table XVI, Pages 312–313
  2. Text Book of Gunnery 1902, Table XII, Page 336
  3. 1910 ft/second firing a 714 lb projectile, with 295 lb Brown Prismatic powder Text Book of Gunnery, 1887. Table XVI, Page 313. Text Book of Gunnery 1902 gives muzlle velocity 1914 ft/second with 295 lb brown powder or 88 lb 8 oz cordite size 30 charge.
  4. Text Book of Gunnery, 1887, Table XIV, Page 308.
  5. Hogg & Thurston 1972, pages 188-189.


  • Hogg, I.V. and Thurston, L.F. (1972). British Artillery Weapons & Ammunition 1914-1918. Ian Allan, London. ISBN 0-7110-0381-5
  • Text Book of Gunnery Archived 4 December 2012 at, 1887. London: Printed for His Majesty's Stationery Office, by Harrison and Sons, St. Martin's Lane
  • Text Book of Gunnery Archived 12 July 2012 at, 1902. London: Printed for His Majesty's Stationery Office, by Harrison and Sons, St. Martin's Lane

External links

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