BL 4-inch Mk IX naval gun

The BL 4-inch Mk IX naval gun[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.

Ordnance BL 4-inch Mk IX gun
On Flower-class corvette HMCS Calgary in World War II
TypeNaval gun
Service history
In service1916–1945
Used by Royal Navy
Royal Canadian Navy

Free French Navy
Hellenic Navy
Royal Indian Navy
Netherlands Navy
Royal New Zealand Navy
Norwegian Navy

South African Navy
WarsWorld War I
World War II
Production history
No. built2,382[1]
Mass2 tons barrel & breech[2]
Barrel length180 inches (4.572 m) bore (45 calibres)

Shell31 pounds (14.1 kg)
Calibre4 inches (101.6 mm)
BreechWelin interrupted screw
Elevation-10 degrees to +30 degrees[3]
Rate of fire10-12 rpm[3]
Muzzle velocity800 metres per second (2,600 ft/s)[2]
Maximum firing range12,660 metres (13,850 yd)[2]


World War I

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 the main armament.

World War II

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

See also


  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.
  3. Campbell, Naval Weapons of WWII, p.38.
  4. DiGiulian
  5. "Jane's Fighting Ships 1919, page 62". Archived from the original on 6 October 2008. Retrieved 18 December 2008.


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