RML 12.5-inch 38-ton gun

Ordnance RML 12.5-inch 38-ton gun
Ordnance RML 12.5-inch 38-ton gun
	Gun at Fort Nelson, Portsmouth, UK
Type	Naval gun; Coast defence gun
Place of origin	United Kingdom
Service history
In service	1875–1905
Used by	Royal Navy
Production history
Designer	Royal Gun Factory
Designed	1874
Manufacturer	Royal Arsenal
Variants	Mk I, Mk II
Specifications
Barrel length	198 inches (5.0 m) (bore)
Shell	800 to 809 pounds (362.9 to 367.0 kg) Palliser, Common, Shrapnel
Calibre	12.5-inch (317.5 mm)
Muzzle velocity	Mk I : 1,425 feet per second (434 m/s); Mk II : 1,575 feet per second (480 m/s)
Maximum firing range	Mk I : 6,000 yards (5,500 m); Mk II : 6,500 yards (5,900 m)

The RML 12.5-inch guns were large rifled muzzle-loading guns designed for British battleships and were also employed for coast defence.

Design

Mark I gun barrel construction

The gun originated from a desire for a longer 12 in (30 cm) gun than the existing RML 12-inch 35-ton gun. Experiments in 1874 with both 12 in (30 cm) and 12.5 in (32 cm) versions 3 ft (91 cm) longer than the existing 12 in (30 cm) gun showed the 12.5 in (32 cm) calibre was more suitable, and further experiments showed a projectile of 800 lb (360 kg) could be fired with a charge of 130 lb (59 kg) of P2 gunpowder without undue strain. The same construction as in the existing 12 in (30 cm) 35-ton gun was used : a mild steel "A" tube toughened in oil, surrounded by wrought iron "B" tube, triple coil in front of the trunnion, coiled breech-piece and breech coil. This was approved in January 1875.^[4]

The gun was rifled on the "Woolwich" pattern of a small number of broad shallow rounded grooves, with 9 grooves increasing from 0 to 1 turn in 35 calibres ( i.e. 1 turn in 437.5 in (1,111 cm)).

Mark II had an enlarged powder chamber and attained higher muzzle velocity and slightly longer range.

This gun was the final development of large British rifled muzzle-loading guns before it switched to breechloaders beginning in 1880. It was succeeded in its class on new battleships by the BL 12 in (30 cm) Mk II gun.

Naval service

Guns were mounted on HMS Dreadnought commissioned in 1879, HMS Agamemnon commissioned in 1883, and HMS Ajax commissioned in 1885, the last British warships completed with muzzle-loading guns.

Ammunition

When the gun was first introduced projectiles had several rows of "studs" which engaged with the gun's rifling to impart spin. Sometime after 1878, "attached gas-checks" were fitted to the bases of the studded shells, reducing wear on the guns and improving their range and accuracy. Subsequently, "automatic gas-checks" were developed which could rotate shells, allowing the deployment of a new range of studless ammunition.

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RML 12.5in Studded Shell, located at Hurst Castle, UK
RML 12.5in Studded Shrapnel Shell Mk I with Attached Gas-Check Mk I
RML 12.5in Studded Palliser Shell Mk III with Attached Gas-Check Mk II
RML 12.5in Studded Common Shell Mk I with Attached Gas-Check Mk II
RML 12.5in Studded Shrapnel Shell Mk I with Attached Gas-check Mk II
RML 12.5in Case Shot Mk III
RML 12.5in Studless Palliser Shell Mk I with Automatic Gas-Check
RML 12.5in Studless Common Shell Mk I with Automatic Gas-Check
RML 12.5in Studless Shrapnel Shell Mk I with Automatic Gas-check

Images 3–9 show the range of ammunition for the RML 12.5-inch gun in 1885.^[5] By this time the gun no longer fired studded ammunition without gas-checks. Instead there were two sets of ammunition available, namely: older studded ammunition with attached gas-checks Mk II, and newer studless ammunition with automatic gas-checks. Case ammunition neither was studded nor required gas-checks. Also by this time, attached gas-checks Mk I as shown in image 2 had been superseded by attached gas-checks Mk II.

Surviving examples

Two at Hurst Castle, UK, originally at Cliff End Battery
At Fort Nelson, Portsmouth, UK, originally at Cliff End Battery
Outside Fort Albert, Isle of Wight
No 22 of 1876 outside Calbourne Mill, Isle of Wight, originally at Cliff End Battery
An unpreserved gun at Fort Delimara, Malta
Gun on replica carriage at Harding's Battery, Gibraltar
Gun number 87 and 95, dated 1878. Now in the ditch at Fort Cunningham, Bermuda

Notes and references

^ Treatise on Construction of Service Ordnance 1877, page 292
^ 1,425 feet/second firing 800-pound projectile with "Battering charge" of 130 pounds "P2" (gunpowder). Treatise on Construction of Service Ordnance 1877, page 347.
^ Muzzle velocity of 1,575 feet/second firing an 809lb 6oz projectile with a charge of 210 pounds Prism2 black powder, is quoted for Mark II gun in "Text Book of Gunnery 1887" Table XVI.
^ Treatise on Construction of Service Ordnance 1877, pages 286-287
^ Handbook for RML 12.5-inch gun (1885) pp. 32-33; Plates XI-XIV

Bibliography

External links

Handbook for the R.M.L. 12.5-inch 38-ton gun, marks I and II : casemate, dwarf, and small port mountings (land service). Great Britain. War Office. London : H.M.S.O. 1885 at State Library of Victoria
Handbook for the 12.5-inch 38-ton R.M.L. gun, marks I and II, casemate, dwarf, and small part mountings land service 1888, 1893, 1899, 1904 at State Library of Victoria
Diagram of gun on small port 6-foot recoil carriage at Victorian Forts and Artillery website
Diagram of gun on Casemate Platform, 6 feet recoil Mark III at Victorian Forts and Artillery website
Diagram of gun on Dwarf 'C' Pivot Mark III at Victorian Forts and Artillery website

[TOA1877page292-1] Treatise on Construction of Service Ordnance 1877, page 292

[2] 1,425 feet/second firing 800-pound projectile with "Battering charge" of 130 pounds "P2" (gunpowder). Treatise on Construction of Service Ordnance 1877, page 347.

[3] Muzzle velocity of 1,575 feet/second firing an 809lb 6oz projectile with a charge of 210 pounds Prism2 black powder, is quoted for Mark II gun in "Text Book of Gunnery 1887" Table XVI.

[4] Treatise on Construction of Service Ordnance 1877, pages 286-287

[5] Handbook for RML 12.5-inch gun (1885) pp. 32-33; Plates XI-XIV

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