BL 4 inch Mk IX naval gun

Ordnance BL 4 inch gun Mk IX
On Flower class corvette HMCS Calgary (K231) in World War II
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^[1]
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
Muzzle velocity	800 metres per second (2,600 ft/s)^[1]
Maximum firing range	12,660 metres (13,850 yd)^[1]

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.

History

World War I

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 ^[2] 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".^[3] Guns were thereafter used in single-gun mountings, typically on smaller ships as primary armament.

World War II

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

On board HMCS Sackville, the last surviving Flower-class corvette, at Halifax, Nova Scotia, Canada
A gun at the entrance to the marina in Hull, UK
A gun at Port Isaac, Cornwall, UK

Notes

↑ 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.

References

Bibliography

Tony DiGiulian, British 4"/45 (10.2 cm) BL Marks IX and X

External links

Wikimedia Commons has media related to BL 4 inch Mk IX naval gun.

British Empire naval weapons of the First World War

Monitor guns	BL 9.2 inch Mk VI BL 9.2 inch Mk VIII BL 9.2 inch Mk X BL 9.2 inch Mk XII BL 12 inch Mk VIII US 14 inch 45 cal BL 18 inch Mk I

Capital ship main armament	Vickers 10 inch 45 cal EOC 10 inch 45 cal BL 12 inch Mk VIII BL 12 inch Mk IX BL 12 inch Mk X BL 12 inch Mk XI & XII EOC 12 inch 45 cal Mk XIII BL 13.5 inch Mk V EOC 14 inch 45 cal Mk I BL 15 inch Mk I

Armoured cruiser main armament	BL 7.5 inch Mk I BL 9.2 inch Mk X BL 9.2 inch Mk XI

Secondary armament and light cruiser main armament	QF 12 pdr 18 cwt QF 14 pounder Maxim-Nordenfelt QF 14 pounder Mk I & II QF 4 inch Mk III BL 4 inch Mk VII QF 4 inch Mk V BL 4 inch Mk IX BL 5.5 inch Mk I QF 6 inch BL 6 inch Mk VII BL 6 inch Mk XI BL 6 inch Mk XII BL 6 inch Mk XIII-XVIII BL 7.5 inch Mk II - Mk V

Destroyer and small cruiser armament	QF 12 pdr 12 cwt Mk II QF 4 inch Mk III BL 4 inch Mk VIII QF 4 inch Mk IV BL 4.7 inch Mk I

Merchant ship armament	QF 4.7 inch Mk I - IV QF 4.7 inch Mk V*

Submarine guns	BL 4 inch Mk XI QF 4 inch Mk XII

Anti-aircraft guns	QF 2 pounder "pom-pom" Mk II QF 3 inch 20 cwt QF 4 inch Mk V

Light weapons	.303 Vickers machine gun QF 3 pounder Hotchkiss QF 3 pounder Vickers QF 6 pounder Hotchkiss

Torpedoes	18 inch Mk V - VIII 21 inch Mk II 21 inch Mk IV

Mines	Spherical Mk I, II and III Vickers Elia mine Type H mine

Anti-submarine weapons	Type A Depth charge Type B Depth charge Type C Depth charge Type D Depth charge Type E Depth charge Type F Depth charge Type G Depth charge Cruiser Mine 7.5 inch howitzer

Landing guns	QF 12 pounder 8 cwt

British Commonwealth naval weapons of the Second World War

Monitor guns	BL 15 inch

Capital ship main armament	BL 14 inch BL 15 inch BL 16 inch

Heavy cruiser main armament	BL 7.5 inch Mk VI BL 8 inch Mk VIII

Secondary armament and light cruiser main armament	QF 4 inch Mk V QF 4.5 inch QF 5.25 inch BL 6 inch Mk XII BL 6 inch Mk XXII BL 6 inch Mk XXIII

Minesweeper, Sloop, Corvette, Frigate and Destroyer armament	QF 6 pounder 10 cwt QF 12 pdr 12 cwt Mk V QF 4 inch Mk IV BL 4 inch Mk IX QF 4 inch Mk XVI QF 4 inch Mk XIX QF 4.5 inch BL 4.7 inch Mk II QF 4.7 inch Mk IX & XII QF 4.7 inch Mk XI

Submarine guns	QF 12 pdr 12 cwt Mk V QF 3 inch 20 cwt QF 4 inch Mk XII & XXII

Anti-aircraft weapons	Unrotated Projectile Holman Projector 20 mm Oerlikon QF 2 pounder "pom-pom" Mk VIII 40 mm Bofors QF 3 inch 20 cwt QF 4 inch Mk V QF 4 inch Mk XVI QF 4.5 inch QF 4.7 inch Mk VIII

Light weapons	.303 Lewis machine gun .50 Vickers Mk III machine gun QF 3 pounder Vickers

Torpedoes	21 inch Mk VII 21 inch Mk VIII 21 inch Mk X 21 inch Mk XI 24.5 inch Mk I

Anti-submarine weapons	Thornycroft depth charge thrower Hedgehog Squid

Small craft armament	Molins 6 pounder Vickers K machine gun 18 inch torpedo

Foreign-sourced weapons	20 mm Oerlikon 40 mm Bofors 3-inch 23 caliber gun (US) 3-inch 50 caliber gun (US) 4-inch 50 caliber Mark 9 gun (US) 5-inch 51 caliber Mark 8 gun (US) Y-gun depth charge projector (US) Mark 8 torpedo (US)

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