BL 4 inch Mk IX naval gun

The BL 4-inch gun Mk IX 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.

Country Name Origin Year
United Kingdom - UK (Great Britain) 1916
Country Name Operational Year Retirement Year
Canada View
France View
Greece View
Netherlands View
South Africa View
United Kingdom - UK (Great Britain) 1916 1945 View
Norway View
New Zealand View

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 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 : gun crew of 23 to each triple". Guns were thereafter used in single-gun mountings, typically on smaller ships as primary 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.

Type Naval gun
Service history
In service 1916 - 1945
Used by  Royal Navy
 Royal Canadian Navy
Free French Navy
Hellenic Navy

Netherlands Navy
New Zealand Navy
Norwegian Navy
South African Navy
Wars World War I
World War II
Specifications
Weight 2 tons barrel & breech
Barrel length 180 inches (4.572 m) bore (45calibres)
Shell 31 pounds (14.1 kg)
Calibre 4 inches (101.6 mm)
Breech Welin interrupted screw
Muzzle velocity 800 metres per second (2,600 ft/s)
Maximum firing range 12,660 metres (13,850 yd)

End notes