BL 4.7-inch 45-calibre naval gun

The BL 4.7-inch, 45-calibre gun (actually a metric 120 mm gun) was a British medium-velocity naval gun introduced in 1918 for destroyers, intended to counter a new generation of heavily armed destroyers that Germany was believed to be developing.

BL 4.7-inch (120 mm), 45-calibre naval gun
"A" gun on destroyer HMAS Stuart, circa. 1930s
TypeNaval gun
Service history
In service1918–1948
Used byUnited Kingdom
WarsWorld War I World War II
Production history
DesignedMk I: 1918
Mk II: 1940[1]
ProducedMk I: 1919
Mk II: 1940[2]
No. builtMk I: 187
Mk II: 32[3]
VariantsMk I, Mk II[note 1]
MassMk I: 7,000 pounds (3,200 kg)
Mk II: 7,028 pounds (3,188 kg)[4]
Barrel length213 inches (5.4 m) bore (45 calibres)

Shell50 pounds (22.7 kg)[5]
Calibre4.724 inches (120 mm)
BreechWelin breech block
Elevation-9.5° to +30°[6]
Traverse-120° to +120°[7]
Rate of fire5-6 RPM[8]
Muzzle velocity2,670 feet per second (814 m/s)[9]
Maximum firing range15,800 yards (14,450 m) at 30°[10]

Description and history

Mk I, of built-up wire-wound construction with propellant charge in a cloth bag went into service beginning in 1918 on destroyers of the new Admiralty type destroyer leader (Scott class) and Thornycroft type leader (Shakespeare class). Some saw service in World War I, but most entered service after the war ended.

It was also mounted on :

Mk II was a monobloc-barrel (i.e. single-piece, typical of small-medium World War II guns) gun of similar performance introduced in World War II to replace the worn-out Mk I guns on surviving ships.

These were the only BL-type 4.7-inch guns in British service, all others have been of the QF-type. They were superseded on new destroyers from 1930 by the QF 4.7-inch Mk IX.


See also

Weapons of comparable role, performance and era


  1. Mk I = Mark 1, Mk II = Mark 2. Britain used Roman numerals to denote Marks (models) of ordnance until after World War II, and used separate number series for BL and QF guns of the same calibre. Hence these were the first (and only) two models of British BL 4.7-inch guns.


  1. DiGiulian
  2. DiGiulian
  3. DiGiulian
  4. DiGiulian
  5. DiGiulian
  6. DiGiulian
  7. DiGiulian
  8. DiGiulian
  9. Mk I : 814 m/s :
  10. Mk I : 14450 metres :


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