BL 4.7-inch (120 mm), 45-calibre naval gun
"A" gun on destroyer HMAS Stuart, circa. 1930s
Type	Naval gun
Service history
In service	1919–1948
Used by	United Kingdom
Wars	World War II
Production history
Designed	Mk I: 1918 Mk II: 1940^[1]
Produced	Mk I: 1919 Mk II: 1940^[2]
No. built	Mk I: 187 Mk II: 32^[3]
Variants	Mk I, Mk II^{[note 1]}
Specifications
Mass	Mk I: 7,000 pounds (3,200 kg) Mk II: 7,028 pounds (3,188 kg)^[4]
Barrel length	213 inches (5.4 m) bore (45 calibres)

Shell	50 pounds (22.7 kg)^[5]
Calibre	4.724 inches (120 mm)
Breech	Welin breech block
Elevation	-9.5° to +30°^[6]
Traverse	-120° to +120°^[7]
Rate of fire	5-6 RPM^[8]
Muzzle velocity	2,670 feet per second (814 m/s)^[9]
Maximum firing range	15,800 yards (14,450 m) at 30°^[10]

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.

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 :

Faulknor-class flotilla leaders as re-gunned in 1918
Thornycroft and Admiralty Modified W-class destroyers completed 1919–1920
Prototype destroyers HMS Ambuscade and HMS Amazon commissioned 1926 & 1927

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 They were superseded on new destroyers from 1930 by the QF 4.7-inch Mk IX.

Ammunition

Mk IIA S.A.P. (semi-armour piercing) shell, 1933

Notes

References

Bibliography

External links

British Empire naval weapons of the First World War

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 BL 14-inch Mk II (US built) BL 15-inch Mk I 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 I – IV BL 13.5-inch Mk V BL 13.5-inch Mk VI 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-pounder 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 Mk I – III 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-pounder 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

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 5.5-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-pounder 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-pounder 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)

Description and history

Ammunition

See also

Weapons of comparable role, performance and era

Notes

References

Bibliography

External links