BL 8-inch Mk I – VII naval gun

The BL 8 inch guns Mark I to Mark VII were the first generations of British rifled breechloaders of medium-heavy calibre. They were initially designed for gunpowder propellants and were of both 25.5 and 30 calibres lengths.

History
Mks I and II were several early proof guns that did not enter British service and Mk V was not made. Limited numbers of 25.5 and 30 calibres guns were produced.

By 1885 the Royal Navy abandoned the 8-inch gun in favour of the 9.2 inch and later the 7.5 inch gun for cruisers, until 1923 when the restrictions of the Washington Naval Treaty led Britain to develop the Mk VIII 8-inch gun in order to arm heavy cruisers with the largest gun allowed by the Treaty.

In the interim Elswick Ordnance continued to develop 8-inch guns in 40 calibre and 45-calibre lengths for export, mainly to Japan.

Mark III
Mk III were low-powered 25-calibres guns mounted on :
 * HMS Bellerophon (1865) as re-gunned in 1885

Mark IV
Mk IV were 30-calibres guns mounted in :
 * Mersey-class cruisers of 1885

Mark VI
Mk VI were 30 calibres guns mounted in :
 * Indian monitors HMS Abyssinia (1870) and HMS Magdala (1870) as re-gunned in 1892

Mark VII
Mk VII were lighter 25-calibres low-powered guns firing a lighter 180-pound projectile used to equip Australian colonial navies and Australian and New Zealand coastal defences in response to expected Russian expansionism in the Pacific (The "Russian scares" of the 1880s).

Naval service
Mk VII guns armed the following Australian colonial gun vessels :
 * HMQS Gayundah of 1884
 * HMCS Protector of 1884
 * HMVS Albert of 1884
 * HMVS Victoria of 1884

Coast defence gun
Mk VII guns were installed on disappearing mountings in Australia and New Zealand as coast-defence guns during the "Russian scares" of the 1880s. In the event, no Russian invasion occurred and the guns were rarely if ever fired.

Four Mk VII coast defence guns were installed at Singapore in the 1880s-1890s : two atop Mount Serapong and two at Fort Tanjong Katong.

Surviving examples

 * Mk VII at North Head, Devonport, New Zealand
 * Mk VII at summit of Mount Victoria, Auckland, New Zealand
 * An unrestored Mk VII disappearing gun at Fort Jervois, Ripapa Island, New Zealand
 * Mk VII at Fort Siloso, Sentosa Island, Singapore See also Photograph at Flickr
 * Mk VII at Royal Artillery Museum, Woolwich, London
 * A Mk VII gun from 1885 on hydro-pneumatic mounting at Fort Queenscliff, Victoria, Australia
 * A pair of Mk VII guns at High Street in Westgarth / Northcote, Victoria, Australia
 * A pair of Mk VII guns at Kangaroo Battery, Rosny, Tasmania, Australia (INCORRECT, these guns are 8in RML, not BL)