The BL 4-inch gun Mk I – Mk VI were a family of early British breech-loading 4-inch naval guns.
History
=== 13 cwt Mk I, 15 calibres === This was the first 4-inch BL gun. With its short (60-inch total) barrel it had a range of only 5,500 yards.
=== 22.5 cwt Mk I, 25 calibres === With its longer barrel (100 inch bore) Mk I had a range of 7,200 yards. Both early Mk I types were quickly withdrawn from service following the explosion of a similar BL 6 inch Mk II gun on board HMS Cordelia in June 1891. Mk I 22.5 cwt continued to be used for training.
=== 26 cwt Mks II - VI, 27 calibres === The improved 27-calibre Mk II gun and subsequent Marks, often referred to as 4 inch 26 cwt, replaced the early Mk I versions in service. The longer barrel (108 inch bore : 27 calibres) gave it a range of 7,700 yards. Mk II guns and later Marks armed the following warships :
HMS Inflexible as re-gunned in 1885 HMS Bellerophon as re-gunned in 1885 Pygmy-class composite screw gunboats of 1888 Redbreast-class gunboats launched in 1889 HMS Alexandra as re-gunned in 1891 Alert-class sloops of 1894 The gun was succeeded in its class from 1895 by the QF 4-inch gun Mk I.
=== QFC 4-inch gun === A small number of these guns were converted to QF to use the same cartridges as the QF 4-inch gun. They were designated Mk I/IV, I/VI etc. depending on which Mark of BL 4-inch had been converted. All had a bore of 27.85 calibres after conversion, with a muzzle velocity of 2,177 ft/second.
== Surviving examples == A gun from 1888 at Explosion! The Museum of Naval Firepower, Gosport from Victorian Forts and Artillery website A gun from HMS Gannet, mounted on top of Calshot Castle at the entrance to Southampton Water from Victorian Forts and Artillery website
== See also == List of naval guns
Notes and references
== Bibliography == Text Book of Gunnery, 1887. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, BY HARRISON AND SONS, ST. MARTIN'S LANE Deprecated link archived 4 December 2012 at archive.today Text Book of Gunnery, 1902. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, BY HARRISON AND SONS, ST. MARTIN'S LANE Deprecated link archived 12 July 2012 at archive.today Tony DiGiulian, British Early 4" (10.2 cm) Breech Loaders
== External links == Handbook for 4-inch B.L. gun mark V and VI land service 1890 at State Library of Victoria Handbook of the 4-inch Gun Marks V and VI. (Land Service.) 1904
Mk V or VI gun as movable fortification gun, on siege overbank carriage. At Victorian Forts and Artillery website Mk I diagram and photos at Victorian Forts and Artillery website