BL 4 inch Mk IX naval gun

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Ordnance BL 4 inch gun Mk IX
HMCS Calgary gun shield badge WWII MC-2166.jpg
On Flower-class corvette HMCS Calgary in World War II
Type Naval gun
Service history
In service 1916 - 1945
Used by

 Royal Navy
Canada Royal Canadian Navy
Free FranceFree French Navy
GreeceHellenic Navy
IndiaRoyal Indian Navy
NetherlandsNetherlands Navy
New ZealandRoyal New Zealand Navy
NorwayNorwegian Navy

South AfricaSouth African Navy
Wars World War I
World War II
Production history
No. built 2,382[1]
Weight 2 tons barrel & breech[2]
Barrel length 180 inches (4.572 m) bore (45 calibres)

Shell 31 pounds (14.1 kg)
Calibre 4 inches (101.6 mm)
Breech Welin interrupted screw
Elevation -10 degrees to +30 degrees[3]
Rate of fire 10-12 rpm[3]
Muzzle velocity 800 metres per second (2,600 ft/s)[2]
Maximum firing range 12,660 metres (13,850 yd)[2]

The BL 4-inch gun Mk IX[note 1] was a British medium-velocity naval gun introduced in 1916 as secondary armament on the Renown-class battlecruisers and Glorious-class "large light cruisers", but which served most notably as the main armament on Flower-class corvettes throughout World War II.


World War I[edit]

Original aft triple mounts on HMS Repulse c. 1916-1917

The gun was based on the barrel of the QF 4 inch Mk V and the breech mechanism of the BL 4 inch Mk VIII [4] and was first introduced in World War I on capital ships as secondary armament in triple-gun mountings, intended to provide rapid concentrated fire. This turned out to be unworkable in practice. Jane's Fighting Ships of 1919 commented, "4-inch triples are clumsy and not liked. They are not mounted in one sleeve; have separate breech mechanism, a gun crew of 23 to each triple".[5] Guns were thereafter used in single-gun mountings, typically on smaller ships as primary armament.

World War II[edit]

Coast defence gun and crew at Fort Crosby near Liverpool, UK, August 1940
Cleaning the breech on transport St Essylt, Suez 1942

In World War II the gun was employed on many small warships such as Flower-class corvettes and minesweepers, primarily for action against surfaced submarines.

This was the last BL 4 inch gun in British service: all subsequent guns have used charges in metal cartridges "QF". It was succeeded on new small warships built in World War II by the QF 4-inch Mk XIX gun which fired a slightly heavier shell at much lower velocity and had a high-angle mounting which added anti-aircraft capability.

Surviving examples[edit]

See also[edit]


  1. ^ Mk IX = Mark 9. Britain used Roman numerals to denote Marks (models) of ordnance until after World War II. Mark IX indicates this was the ninth model of BL 4-inch gun.


  1. ^ Campbell, Naval Weapons of WWII, p.42-43.
  2. ^ a b c
  3. ^ a b Campbell, Naval Weapons of WWII, p.38.
  4. ^ DiGiulian
  5. ^ Jane's Fighting Ships 1919, page 62


External links[edit]