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Anti-submarine mortar

BL 7.5-inch naval howitzer
On SS Boonah
Type	Anti-submarine mortar
Place of origin	United Kingdom
Service history
In service	1917 - 192?
Used by	British Empire
Wars	World War I
Specifications
Mass	Gun & breech 812 pounds (368 kg)
Barrel length	Bore 63.75 inches (1.619 m)

Shell	HE 100 pounds (45.4 kg)
Calibre	7.5-inch (191 mm)
Breech	single-motion interrupted screw
Muzzle velocity	480 feet per second (146 m/s)
Maximum firing range	2,100 yards (1,920 m)
Filling	TNT
Filling weight	43 pounds (19.5 kg)

The BL 7.5-inch howitzer (naval) was a British anti-submarine mortar developed during World War I.

History

The weapon was developed together with other similar devices early in 1917 and went into service in June 1917 in response to German unrestricted submarine warfare. It was mounted on merchant ships and patrol vessels. By 10 December that year, 377 were in service.

The shell was fired at the submarine either on the surface or submerged - hence it had attributes of both armour-piercing shell and depth charge. It was designed to first penetrate the submarine's outer hull without breaking up, and then detonate against the inner hull after a 2-second delay, destroying the submarine. However the small weight of the shell limited its effectiveness, and the anti-submarine mortar did not become a truly successful weapon until the advent of the multiple-projectile Hedgehog during World War II.

Nonetheless Admiral John Jellicoe, writing a few years after the gun had gone into service, commented: "This weapon, although not very popular at first, soon, however, proved its value, when employed both from patrol craft and from merchant ships."

Two were mounted on HMS Vindictive and used to bombard German defences during her participation in the Zeebrugge raid of 23 April 1918.

Similar weapons

12 cm/12 short naval gun - A Japanese anti-submarine gun used during World War II.
20 cm/12 short naval gun - A Japanese anti-submarine gun used during the latter half of World War II.
8-inch Mark 7 & Mark 8 - Two American anti-submarine guns designed late in World War I that never entered service.

Notes and references

^ Hogg and Thurston 1972, Pages 148-149
Standard shell was 100 lb, containing 43 lb TNT. In early 1918 a 500 lb stick bomb containing 250 lb TNT was developed, with a range of 300 yards. Hogg & Thurston 1972, page 148
^ Jellicoe, 1920. Chapter III

Bibliography

I.V. Hogg & L.F. Thurston, British Artillery Weapons & Ammunition 1914–1918. London: Ian Allan, 1972
Admiral John Jellicoe, "The Crisis of the Naval War", published 1920

v t e 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

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