BL 4-inch Mk VIII naval gun

The BL 4-inch Mark VIII naval gun[note 1] was a British medium-velocity wire-wound naval gun introduced in 1908 as an anti-torpedo boat gun in smaller ships whose decks could not support the strain of the heavier and more powerful Mk VII gun.[2]

Ordnance BL-4-inch Mk VIII naval gun
Forward gun of HMS Defender
TypeNaval gun
Service history
In service1908–1945
Used byUnited Kingdom
WarsWorld War IWorld War II
Production history
No. builtMk VIII: 246
Mk XI: 30[1]
VariantsMk VIII – Mk XI[1]
Mass2,912 pounds (1,320 kg) (barrel & breech)[2]
Barrel length159.2 inches (4.044 m) bore (40 calibres)[2]

Shell31 pounds (14.06 kg) Common pointed, Common lyddite[2]
Calibre4 inches (101.6 mm)
BreechWelin, single-motion screw[2]
Elevation-10° to +20°[1]
Rate of fire6-8 RPM[1]
Muzzle velocity2,287 feet per second (697 m/s)[3]
Maximum firing range10,210 yards (9,340 m)[1]

Mk VIII history

The gun succeeded the QF 4-inch Mk III, whose 25-pound (11 kg) shell had been considered insufficiently powerful for its intended role. The BL Mk VIII fired a 31-pound (14 kg) shell. It armed the following warships :

The gun was succeeded in its class from 1911 by the QF 4-inch Mk IV.

In World War II many guns were used to arm merchant ships.

Mk XI submarine gun

A Mark XI-variant was adapted to arm the K-class submarines laid down 1915.

See also


  1. Mark VIII = Mark 8. Mark XI = Mark 11. Britain used Roman numerals to denote marks (models) of ordnance until after World War II. This was the eighth model of British BL 4-inch gun.


  1. DiGiulian
  2. HANDBOOK for the 4" Mark VII. and VIII. B.L. Guns 1913
  3. 2287 ft/second firing a 31 lb 3 CRH projectile, using 5 lb 4 oz cordite MD size 16 propellant. HANDBOOK for the 4" Mark VII. and VIII. B.L. Guns 1913.


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