BL 12 inch naval gun Mk VIII

Ordnance BL 12 inch gun Mk VIII
Muzzle of gun on HMS Canopus, 1916
Type	Naval Gun, Coastal Defence
Place of origin	United Kingdom
Service history
In service	1895–1910s
Used by	Royal Navy
Wars	World War I
Production history
Designer	Woolwich Arsenal
Manufacturer	Vickers
Variants	Mk VIII, VIIIe, VIIIv
Specifications
Weight	46 tons barrel & breech
Barrel length	35 ft 5 in (10.80 m) (35.43 calibres)
Shell	850 lb (390 kg)
Calibre	12-inch (304.8 mm)
Muzzle velocity	2,367 ft/s (721 m/s)
Effective firing range	10,000 yd (9,100 m)

The BL 12 inch naval gun Mark VIII was one of the first large British rifled breech-loading naval guns designed for the higher pressures generated by the new cordite propellant of the 1890s, and Britain's first large wire-wound gun. It represented a major advance compared to previous British guns.

The gun was installed on the Majestic-class battleships from 1895 and on the Canopus-class battleships from 1899. During World War I guns removed from the obsolete Majestic class were mounted in Lord Clive-class monitors for shore bombardment.

From 1921 to 1926 two guns from the decommissioned battleship HMS Illustrious were in service in the Tyne Turrets for coast defence, north and south of the mouth of the River Tyne in the northeast of England.

During bombardment service when mounted in the Lord Clive-class monitors deposition of copper from the projectile driving bands needed frequent removal. However, problems with the inner liners were more serious. The continual drag of the driving bands caused the liner to be gradually stretched forward. The resulting protrusion at the muzzle could simply be cut off, but in addition the liner began to form a ridge in the barrel near the shoulders of the outer ‘A’ tube, where the inner ‘A’ tube was keyed to the outer. The ridge accumulated copper from the driving bands, which could give sufficient retardation to the projectile to start the fuze, which resulted in a premature detonation either within the bore, or soon after leaving the muzzle. This happened several times during bombardment service, including an occasion when Lord Clive showered pieces of shell over the French destroyer Aventurier. The ‘steel choke’ restriction could be temporarily removed by rubbing down with an emery-covered block pulled back and forth in the bore, but the only permanent cure was to fit new guns with a modified design of liner, which had a different arrangement of internal shoulders.