BL 6 inch gun Mk V

Last updated
Armstrong BL 6-inch 30 calibre gun

Armstrong cannon, Chulachomklao fort.jpg

Disappearing gun at Fort Chulachomklao, Thailand
Type Coast defence gun
Place of origin United Kingdom
Service history
In service 1884 - 1945 [1]
Used by United Kingdom
Australian Colonies
New Zealand
Siam
Production history
Designer Elswick Ordnance Company (EOC)
Manufacturer EOC
Unit cost £3,400 [2]
Specifications
Weight 5 tons barrel & breech [3]
Barrel  length 183.5 inches (4,661 mm) bore (30.58 calibres); [4]
192 inches (4,877 mm) bore and chamber (32 calibres) [5]

Shell 100 pounds (45.36 kg) [4]
Calibre 6-inch (152.4 mm)
Breech 3 motion interrupted screw. Elswick cup obturation
Muzzle velocity 1,890 feet per second (576 m/s) [6]
Maximum firing range 8,000 yards (7,300 m) [7]

The BL 6 inch gun Mk V [note 1] was an early Elswick Ordnance Company breech-loading naval gun originally designed to use the old gunpowder propellants. They were used for coast defence around the British Empire.

Gunpowder explosive most commonly used as propellant in firearms

Gunpowder, also known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur (S), charcoal (C), and potassium nitrate (saltpeter, KNO3). The sulfur and charcoal act as fuels while the saltpeter is an oxidizer. Because of its incendiary properties and the amount of heat and gas volume that it generates, gunpowder has been widely used as a propellant in firearms, artillery, rockets, and fireworks, and as a blasting powder in quarrying, mining, and road building.

Contents

Description and service

Gun construction and rifling diagram BL 6 inch Mk V gun diagram.jpg
Gun construction and rifling diagram

This was an Elswick Ordnance export design, completely different from and longer (30-calibres, 183.5 inch bore) than the contemporary 26-calibres British naval service 6-inch Mk III, IV and VI guns designed by the Royal Gun Factory, although it fired the same 100-pound projectiles. The gun was of a complex all-steel built-up construction, of a steel A-tube surrounded by multiple steel hoops, breech-piece and jacket.

A hoop gun is a gun production technique that uses multiple layers of tubes to form a built-up gun. The innermost tube has one or more extra tubes wrapped around the main tube. These outer tubes are preheated before they are slid into position. As the outer tubes cool they naturally contract. This pre-stresses the main tube so it can withstand greater internal pressures.

Several were acquired by the British government for coast defence in the UK and were given the designation 6-inch gun Mark V. The breech fittings and firing mechanism were modified in British service to standardize them with the British service guns, Mark IV and VI. The breech-screw was locked by turning to the left, unlike standard service guns made by the Royal Gun Factory, which all locked to the right. Rifling consisted of 28 grooves of the polygroove "Elswick section" type, increasing from 0 to 1 turn in 30 calibres (i.e. 1 turn in 180 inches) at the muzzle. [8]

Rifling

In firearms, rifling is the helical groove pattern that is machined into the internal (bore) surface of a gun's barrel, for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting. This spin serves to gyroscopically stabilize the projectile by conservation of angular momentum, improving its aerodynamic stability and accuracy over smoothbore designs.

Mk V in the upper casemate battery at Georges Head, Sydney, 1892 BL 6 inch Mk V gun Georges Head 1892.jpg
Mk V in the upper casemate battery at Georges Head, Sydney, 1892

They were also exported for use as coast-defence guns in Hong Kong, New Zealand, Australian colonies and Siam (Thailand), typically as disappearing guns.

Disappearing gun

A disappearing gun, a gun mounted on a disappearing carriage, is an obsolete type of artillery which enabled a gun to hide from direct fire and observation. The overwhelming majority of carriage designs enabled the gun to rotate backwards and down behind a parapet, or into a pit protected by a wall after it was fired; a small number were simply barbette mounts on a retractable platform. Either way, retraction lowered the gun from view and direct fire by the enemy while it was being reloaded. It also made reloading easier, since it lowered the breech to a level just above the loading platform, and shells could be rolled right up to the open breech for loading and ramming. Other benefits over non-disappearing types were a higher rate of repetitive fire and less fatigue for the gun crew.

QFC conversion

QFC gun, Albany defences, March 1943 QFC 6 inch gun Albany 1943 AWM 029664.jpeg
QFC gun, Albany defences, March 1943

During the 1890s, when the new "QF" technology of loading propellant charges in brass cases to increase the rate of fire was in favour, 4 guns were returned from New South Wales, Australia to the UK to be converted to QF.

2 of the resulting QFC guns are known to have been still in commission until 1945, in the Princess Royal Fortress defending the port of Albany, Western Australia. [9]

Albany, Western Australia City in Western Australia

Albany is a port city in the Great Southern region of Western Australia, 418 km SE of Perth, the state capital. Albany is the oldest colonial settlement in Western Australia, predating Perth and Fremantle by over two years.

See also

Surviving examples

Notes

  1. Mk V = Mark 5. Britain used Roman numerals to designate Marks (models) of ordnance until after World War II. Hence this was the fifth model of BL 6-inch gun in British service.

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References

  1. 2 QFC guns were in service until 1945 at Albany, Western Australia
  2. Unit price for 13 Mk V guns purchased by New Zealand in 1885. 1885 New Zealand Harbour defences (Table showing amount required for) Laid on the Table by the Hon. Mr Ballance, with the Leave of the House.
  3. Text Book of Gunnery 1902
  4. 1 2 Text Book of Gunnery 1902, Table XII
  5. Text Book of Gunnery 1887, Table XVI
  6. Mk V gun is quoted with mv of 1920 feet/second in Text Book of Gunnery 1887, and 1890 ft/sec in the 1902 edition.
  7. Text Book of Gunnery 1902 quotes 10,000 yards for Mks III, IV, VI and 8,000 yards for Mk V.
  8. "Treatise on Construction of Service Ordnance, 1893", pages 263-264
  9. Peter Dunn, "two emplaced at the fortress from 1938 to 1945. It was originally from South Head - Sydney and was one of the four BL guns from the Colony of NSW which was sent to England in the late part of the 19th Century to be converted to QF"
  10. http://www.thaifolk.com/doc/attract/pomprajul/pomprajul_e.asp

Bibliography