BL 4-inch Mk I – VI naval gun

The BL 4-inch gun Mk I – Mk VI[5] were a family of early British breech-loading 4-inch naval guns.

Ordnance BL 4-inch gun Mk I – Mk VI
TypeNaval gun
Place of originUnited Kingdom
Service history
In service1880s – 190?
Used byUnited Kingdom
Specifications
Barrel lengthMk 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]
Shell25 pounds (11.34 kg)[2]
Calibre4-inch (101.6 mm)
Breech3-motion screw
Muzzle velocityMk 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 rangeMk II-VI 7,700 yards (7,000 m)[2]

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With its longer barrel (100 inch bore) Mk I had a range of 7,200 yards.[1] Both early Mk I types were quickly withdrawn from service following the explosion of a similar BL 6 inch Mk II gun on board HMS Cordelia in June 1891.[1] Mk I 22.5 cwt continued to be used for training.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

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

See also

Notes and references
  1. DiGiulian
  2. Text Book of Gunnery, 1902
  3. 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
  4. 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)
  5. 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
  6. Text Book of Gunnery 1902

Bibliography
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