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Ordnance RML 7 inch gun
Ordnance RML 7 inch gun
	; 7 inch 6½ ton Mk I gun and crew on HMS Minotaur; ;
Type	; Naval gun; Coast defence gun;
Place of origin	United Kingdom
Service history
Used by	Royal Navy
Production history
Designer	Royal Gun Factory
Designed	1865 (7 & 6½ ton); 1874 (90 cwt)
Manufacturer	Royal Arsenal
Unit cost	£425;
Variants	7 ton Mks I - IV; 6½ ton Mks I - III; 90 cwt
Specifications
; Barrel length	7 ton : 126 inches (3,200 mm); 6½ ton & 90 cwt : 111 inches (2,800 mm);
Shell	112 to 115 pounds (51 to 52 kg) Palliser, Common, Shrapnel; 160 pounds (73 kg) double common shell
Calibre	7-inch (177.8 mm)
Muzzle velocity	7 ton : 1,561 feet per second (476 m/s); 6½ ton : 1,525 feet per second (465 m/s); 90 cwt : 1,325 feet per second (404 m/s)
Maximum firing range	5,500 yards (5,000 m)

The RML 7 inch guns were various designs of medium-sized rifled muzzle-loading guns used to arm small to medium-sized British warships in the late 19th century, and some were used ashore for coast defence.

Design and history

"Woolwich" rifling introduced in 1865

These guns were the first to incorporate the new "Woolwich" rifling system, a modification of the French system, of from 3 - 9 broad shallow grooves after Britain abandoned the Armstrong "shunt" rifling system in May 1865 : "...M.L. 7-inch guns in course of manufacture were rifled on this principle, upon which all of our heavy pieces since have been rifled. The 7-inch referred to, and introduced into the service in 1865, were the first of the so-called Woolwich guns, which then meant "wrought iron M.L. guns built up on Sir W. Armstrong's principle, improved upon by hooking the coils over one another, and having solid ended steel barrels, rifled on the system shown above, for studded projectiles".^[4]

All versions were constructed of a steel A tube surrounded by various numbers and thicknesses of wrought-iron coils. Rifling was 3 grooves with a uniform 1 turn in 35 calibres i.e. in 245 inches.^[2]

The diagrams below show the progression from the original expensive Armstrong construction in Mk I of multiple relatively thin coils, through to the simplified and cheaper Woolwich design of Mk III.

The 4 Marks of 7 ton gun

The 3 Marks of 6½ ton gun

90 cwt gun

RML 7 inch 7 ton gun

Remains of a 7-ton Mk III gun on Flat Holm island, UK

This was a coast defence gun introduced in 1865 to replace the failed RBL 7 inch Armstrong gun.Three marks were produced.

RML 7 inch 6½ ton gun

This was a naval gun introduced in 1865 "...as a broadside or pivot gun for frigates, to replace the 7-inch B.L. and 68-pr S.B. guns, and is now very extensively used, 331 having been made... These guns are in total length 18 inches shorter than the land service [i.e. 7-ton] 7-inch gun, being a length more suited to the requirements of the Navy".^[5]

The following warships were armed with the gun :

Amazon-class sloops in commission from 1865

HMS Bellerophon commissioned in 1866

HMS Vixen commissioned 1866

HMS Viper commissioned 1866

Minotaur-class ironclads commissioned 1867

Eclipse-class sloops in commission from 1867

Defence-class ironclads (as re-gunned in 1867)

HMS Enterprise & HMS Research (as re-gunned in 1868)

Warrior-class ironclads (as re-gunned in 1867-1868)

Hector-class ironclads (from 1868)

HMS Achilles (as re-gunned in 1868)

HMS Inconstant in commission from 1869

HMS Shah in commission from 1876

Briton-class screw corvettes in commission from 1871

RML 7 inch 90 cwt gun

This was a lighter (90 cwt = 4½ tons) low-powered naval gun introduced in 1874 as a broadside gun on unarmoured vessels, and not intended for attacking armour plate. Early models were made by simply turning off some of the jacket around 7-inch 6½ ton guns, as firing with reduced charges placed less strain on the coils. Some new guns were made to similar design.

The following warships were armed with the gun :

Osprey-class sloops in commission from 1874

HMS Raleigh in commission from 1874

Fantome-class sloops in commission from 1874

Bacchante-class corvettes in commission from 1877

Condor-class gunvessels in commission from 1877

Ammunition

The primary projectile for 7 ton and 6½ ton guns was Palliser shot or shell for attacking armoured warships, fired with a large "battering" charge for maximum velocity. All guns were also equipped with shrapnel shells for anti-personnel use and explosive common shells for attacking unarmoured targets. The "double" common shell was much longer than the standard common shell, and hence contained approximately twice as much gunpowder. It was unstable in flight and hence inaccurate beyond 2,000 yards but was considered useful for attacking wooden warships at ranges below 2,000 yards.^[6]

Mk III Palliser shell

Mk VI Palliser shot

Mk III shrapnel shell

Mk V common shell

Mk III double common shell

This was the only RML heavy gun not to be issued with gas-checks.

Surviving examples

Restored 6½ ton Mk I Numbers 148 & 163 at Garden Island Rockingham, Western Australia (Fleet Base West). For restoration story see http://www.defence.gov.au/news/navynews/editions/4719/feature/feature06.htm

Several 6½ ton Mk I guns on Ascension Island

6½ ton Mk I at Fort Siloso, Singapore

6½ ton Mk III of 1869, at Elizabeth Castle, Jersey, UK

Remains of several 7 ton Mk III guns on Flat Holm island, UK

Nine 7 ton Mk III guns on Steep Holm island, UK

A 7-ton Mk I gun at The Citadel, Nova Scotia, Canada

A 6½ ton Mk I gun on Signal Hill (Cape Town), South Africa.

Notes and references

^ Unit cost of £424 11 shillings 10 pence is quoted for the 7 inch 6½ ton gun in "The British Navy" Volume II, 1882, by Sir Thomas Brassey. Page 38

^ ^a^b Treatise on construction of ordnance in the British service, 1877, Table XXIX

^ Treatise on Ammunition 1877 and Treatise on construction of ordnance in the British service, 1877 describe a 115-pound projectile; Text Book of Gunnery 1887 and Brassey's Naval Annual 1888 describe a 112-pound 1 oz projectile. 112 lb 1 oz appears to be the weight of the empty Palliser shell i.e. without gunpowder filling which was typically 2 lb 10 oz. By 1887 palliser shell had been discontinued and existing shell converted to shot by removing the gunpowder - hence old Palliser ammunition would then be 112 lb 1 oz.

^ Treatise on construction of ordnance in the British service, 1877, Page 91

^ Treatise on construction of ordnance in the British service, 1877, Page 269

^ Treatise on Ammunition 1877, Page 189

Bibliography

Treatise on the construction and manufacture of ordnance in the British service. War Office, UK, 1877

Treatise on Ammunition. War Office, UK, 1877^{[permanent dead link]}

Victorian Forts Website. Rifled Muzzle Loading Guns

Sir Thomas Brassey, The British Navy, Volume II. London: Longmans, Green and Co. 1882

Text Book of Gunnery, 1887. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, BY HARRISON AND SONS, ST. MARTIN'S LANE

Brassey's Naval Annual, 1888

External links

Handbook for the 7-inch R.M.L. guns of 6½ and 7 tons on sliding and Moncrieff carriage land service, 1888 at State Library of Victoria

Diagram showing 7 ton Mk III gun on Moncrieff mounting Mk I

Diagram showing 7 ton Mk III gun on Moncrieff mounting Mk II

[1] Unit cost of £424 11 shillings 10 pence is quoted for the 7 inch 6½ ton gun in "The British Navy" Volume II, 1882, by Sir Thomas Brassey. Page 38

[ReferenceA-2] Treatise on construction of ordnance in the British service, 1877, Table XXIX

[3] Treatise on Ammunition 1877 and Treatise on construction of ordnance in the British service, 1877 describe a 115-pound projectile; Text Book of Gunnery 1887 and Brassey's Naval Annual 1888 describe a 112-pound 1 oz projectile. 112 lb 1 oz appears to be the weight of the empty Palliser shell i.e. without gunpowder filling which was typically 2 lb 10 oz. By 1887 palliser shell had been discontinued and existing shell converted to shot by removing the gunpowder - hence old Palliser ammunition would then be 112 lb 1 oz.

[4] Treatise on construction of ordnance in the British service, 1877, Page 91

[5] Treatise on construction of ordnance in the British service, 1877, Page 269

[6] Treatise on Ammunition 1877, Page 189

v t e British Empire naval weapons of the Victorian era
Smoothbore muzzle-loading cannons	18-pounder 24-pounder 32-pounder 58 cwt 68-pounder Somerset cannon
Smoothbore muzzle-loading shell guns	8 inch 10-inch 86 cwt
Mortars	10-inch Blomefield 13-inch Blomefield
Howitzers	12-pounder Millar 24-pounder Millar
Rifled breechloaders (Armstrong)	RBL 9 pounder RBL 20 pounder RBL 40 pounder RBL 7 inch 110 pounder
Rifled muzzle-loaders (Lancaster)	68-Pounder Lancaster gun
Rifled muzzle-loaders (converted)	RML 64 pounder 71 cwt
Rifled muzzle-loaders (Woolwich)	RML 9 pounder 8 cwt RML 64 pounder 64 cwt RML 7 inch RML 8 inch RML 9 inch RML 10 inch RML 11 inch RML 12 inch 25 ton RML 12 inch 35 ton RML 12.5 inch RML 16 inch
Breech-loaders (new pattern)	BL 4 inch BL 5 inch BL 6 inch 80 pounder BL 6 inch Mk II – VI BL 8 inch BL 9.2 inch Mk I – VII BL 9.2 inch Mk VIII BL 10 inch BL 12 inch Mk I – VII BL 12 inch Mk VIII BL 13.5 inch BL 16.25 inch
Quick-firing guns	QF 3-pounder Hotchkiss QF 6-pounder Hotchkiss QF 6 pounder Nordenfelt QF 12-pounder 12 cwt Mk I QF 4 inch QF 4.7 inch QF 6 inch
Light weapons	Gatling gun Gardner gun Nordenfelt gun 1-inch Nordenfelt gun
Torpedoes	Whitehead torpedo

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