|Ordnance RML 9 inch 12 ton gun|
Mk IV or V on central battery ironclad HMS Iron Duke circa. 1870s
Coast defence gun
|Place of origin||United Kingdom|
|In service||1865 - 1922 (Mk VI)|
|Used by||Royal Navy|
|Wars||Bombardment of Alexandria (1882)|
|Variants||Mk I - VI|
|Barrel length||125 inches (3.2 m) (bore)|
|Shell||Mk I - V : 250 to 256 pounds (113.4 to 116.1 kg) Palliser, Common, Shrapnel|
Mk VI : 360 pounds (163.3 kg) AP
|Calibre||9-inch (228.6 mm)|
|Muzzle velocity||1,420 feet per second (430 m/s)|
The RML 9 inch guns Mark I - Mark VI were large rifled muzzle-loading guns used as primary armament on smaller British ironclad battleships and secondary armament on larger battleships, and also ashore for coast defence.
Mark I, introduced in 1865, incorporated the strong but expensive Armstrong method of a steel A tube surrounded by multiple thin wrought-iron coils which maintained the central A tube under compression, and a forged steel breech-piece. 190 were made.
Mark II in 1866 incorporated the modified "Fraser" design. This was an economy measure, intended to reduce the costs incurred in building to the Armstrong design. It incorporated fewer but heavier wrought-iron coils but retained the Armstrong forged breech-piece. Only 26 were made.
Mark III in 1866-1867 eliminated the Armstrong forged breech piece and hence fully implemented the Fraser economy design. It consisted of only 4 parts : steel A tube, cascabel, B tube and breech coil. 136 were made.
Mark IV, introduced 1869, and V incorporated a thinner steel A tube and 2 breech coils. The explanation for separating the heavy breech coil of Mk III into a coiled breech piece covered by a breech coil was "the difficulty of ensuring the soundness of the interior of a large mass of iron".
Mk VI high-angle gun
In the late 1880s and early 1890s a small number of guns were adapted as high-angle coast defence guns around Britain : known battery locations were Tregantle Down Battery at Plymouth, Verne High Angle Battery at Portland and Steynewood Battery at Bembridge on the Isle of Wight.
The idea behind these high-angle guns was that the high elevation gave the shell a steep angle of descent and hence enabled it to penetrate the lightly armoured decks of attacking ships rather than their heavily armoured sides. To increase accuracy the old barrels were relined and given modern "polygroove" rifling : 27 grooves with a twist increasing from 1 turn in 100 calibres to 1 turn in 35 calibres after 49.5 inches. These guns fired a special 360-pound armour-piercing shell to a range of 10,500 yards using a propellant charge of 14 lb Cordite Mk I size 7½, remained in service through World War I and were not declared obsolete until 1922.
Some guns were bored out and relined in 10-inch calibre. A battery of six such guns is known to have been mounted at Spy Glass Battery on the Rock of Gibraltar, and six guns at Gharghur, Malta.
When the gun was first introduced in 1865, projectiles had several rows of projecting "studs" which engaged with the gun's rifling to impart spin. From the mid-late 1870s, spin was imparted by "gas checks" connected to the base of the projectile which engaged the rifling grooves, making studs unnecessary, and hence the shells were designated "studless".
The gun's primary projectile was "Palliser" shot or shell, an early armour-piercing projectile for attacking armoured warships. A large "battering charge" of 50 pounds "P" (pebble) or 43 pounds "R.L.G." (rifle large grain) gunpowder was used for the Palliser projectile to achieve maximum velocity and hence penetrating capability.
Common (i.e. ordinary explosive) shells and shrapnel shells were fired with the standard "full service charge" of 30 pounds R.L.G. gunpowder or 33 pounds P (pebble) gunpowder, as for these velocity was not as important.
- Needles Old Battery, Isle of Wight, UK
- A gun from the Needles Old Battery, now outside Southsea Castle, Portsmouth, UK
- Hurst Castle, UK
- Mk V No. 592 at South Head, Sydney, Australia
- MK I No. 1670 of 1867 at Fort Queenscliff, Victoria, Australia
- No.s 1679 & 1683 at The Strand, Williamstown, Victoria, Australia
- No.s 1669 & 1675 at Fort Gellibrand, Victoria, Australia
- Mk V gun of 1872 at Whampoa, Kowloon, Hong Kong
- At York Redoubt National Historic Site, Halifax, Nova Scotia, Canada
- A gun at The Citadel, Quebec, Canada
Notes and references
- Unit cost of £739 17 shillings 8 pence is quoted in "The British Navy" Volume II, 1882, by Sir Thomas Brassey. Page 38
- Treatise on Construction of Service Ordnance 1877, page 292
- 250 lb projectile is quoted in 1877 Treatise on Ammunition; 253 lb 5 oz in Text Book of Gunnery 1887; 256 lb in Text Book of Gunnery 1902
- Hogg & Thurston 1972; Text Book of Gunnery 1902
- 1,420 feet/second firing 250-pound projectile with "Battering charge" of 50 pound "P" (gunpowder). Treatise on Construction of Service Ordnance 1877, page 348
- Mark I - Mark VI = Mark 1 thru to Mark 6. Britain used Roman numerals to denote Marks (models) of ordnance until after World War II. Hence this article describes the six models of RML 9-inch guns.
- Holley states that Daniel Treadwell first patented the concept of a central steel tube kept under compression by wrought-iron coils.. and that Armstrong's assertion that he (Armstrong) first used a wrought-iron A-tube and hence did not infringe the patent, was disingenuous, as the main point in Treadwell's patent was the tension exerted by the wrought-iron coils, which Armstrong used in exactly the same fashion. Holley, Treatise on Ordnance and Armour, 1865, pages 863-870
- Treatise on Construction of Service Ordnance 1877, pages 92-93 and 277-280
- Hogg & Thurston 1972, page 158-159
- Treatise on Ammunition 1877, page 220
- Treatise on the construction and manufacture of ordnance in the British service. War Office, UK, 1877
- Text Book of Gunnery, 1887. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, BY HARRISON AND SONS, ST. MARTIN'S LANE
- Text Book of Gunnery, 1902. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, BY HARRISON AND SONS, ST. MARTIN'S LANE
- Treatise on Ammunition. 2nd Edition 1877. War Office, UK.
- Treatise on Ammunition, 4th Edition 1887. War Office, UK.
- Sir Thomas Brassey, The British Navy, Volume II. London: Longmans, Green and Co. 1882
- I.V. Hogg & L.F. Thurston, British Artillery Weapons & Ammunition 1914-1918. London: Ian Allan, 1972.
- Alexander Lyman Holley, "A Treatise on Ordnance and Armor" published by D Van Nostrand, New York, 1865
- "The High Angle Mountings" at Victorian Forts website
|Wikimedia Commons has media related to RML 9 inch 12 ton Gun.|
- Diagram of gun on Moncrieff disappearing mounting, at Victorian Forts website
- Diagram of gun on Casemate "A" Pivot mounting, at Victorian Forts website
- Diagram of gun on "C" Pivot, at Victorian Forts website
- Diagram of gun on Dwarf "A" Pivot, at Victorian Forts website
- Diagram of gun on High Angle mounting, at Victorian Forts website
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