BL 4-inch Mk I – VI naval gun

Naval gun

Ordnance BL 4-inch gun Mk I – Mk VI

Type	Naval gun
Place of origin	United Kingdom
Service history
In service	1880s – 190?
Used by	United Kingdom
Specifications
Barrel length	Mk I 22.5cwt : 100 inches (2.540 m) bore (25 calibres)^[1] Mk II – VI : 108 inches (2.743 m) bore (27 calibres)^[2] 120 inches total^[1]

Shell	25 pounds (11.34 kg)^[2]
Calibre	4-inch (101.6 mm)
Breech	3-motion screw
Muzzle velocity	Mk I 13cwt : 1,180 feet per second (360 m/s)^[3] Mk II – VI : 1,900 feet per second (580 m/s)^[4]
Maximum firing range	Mk II-VI 7,700 yards (7,000 m)^[2]

The BL 4-inch gun Mk I – Mk VI^[5] 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.^[1]

22.5 cwt Mk I, 25 calibres

With its longer barrel (100 inch bore) Mk I had a range of 7,200 yards.^[1] Both early Mk I types were quickly withdrawn from service following the explosion of a similar BL 6 inch Mk II gun on board HMS Cordelia in June 1891.^[1] Mk I 22.5 cwt continued to be used for training.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.^[6]

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.^[2]

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

Notes and references

^ ^a ^b ^c ^d ^e DiGiulian
^ ^a ^b ^c ^d Text Book of Gunnery, 1902
^ Mk I 13cwt gun : 1180 ft/sec firing 25 pound projectile with 3lb 4oz RLG2 (gunpowder). Text Book of Gunnery 1887, Table XVI page 313
^ Mk II – VI 1,900 ft/s with 25 lb (11 kg) projectile, using 12 lb (5.4 kg) S.P. (gunpowder) or 3 lb 1 oz (1.4 kg) cordite MK I size 5 propellant (Text Book of Gunnery, 1902)
^ Mk I – Mk VI = Marks 1 through to Mark 6. Britain used Roman numerals to denote Marks (models) of ordnance until after World War 2. This article covers the first six models of British BL 4-inch naval guns
^ Text Book of Gunnery 1902

Bibliography

Text Book of Gunnery, 1887. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, BY HARRISON AND SONS, ST. MARTIN'S LANE 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 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

Wikimedia Commons has media related to BL 4 inch Mk I - VI naval gun.

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

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