The gun originated from a desire for a longer 12in (30cm) gun than the existing RML 12-inch 35-ton gun. Experiments in 1874 with both 12in (30cm) and 12.5in (32cm) versions 3ft (91cm) longer than the existing 12in (30cm) gun showed the 12.5in (32cm) calibre was more suitable, and further experiments showed a projectile of 800lb (360kg) could be fired with a charge of 130lb (59kg) of P2 gunpowder without undue strain. The same construction as in the existing 12in (30cm) 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 437.5in (1,111cm)).
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 12in (30cm) 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.
↑ 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
This article explains terms used for the British Armed Forces' ordnance (weapons) and ammunition. The terms may have slightly different meanings in the military of other countries.
The 100-ton gun was a 17.72 inches (450 mm) rifled muzzle-loading (RML) gun made by Elswick Ordnance Company, the armaments division of the British manufacturing company Armstrong Whitworth, owned by William Armstrong. The 15 guns Armstrong made were used to arm two Italian battleships and, to counter these, British fortifications at Malta and Gibraltar.
The BL 9.2-inch Mk I–VII guns were a family of early British heavy breechloading naval and coast defence guns in service from 1881 to the end of World War I. They were originally designed to use the old gunpowder propellants.
The BL 6-inch gun Marks II, III, IV and VI were the second and subsequent generations of British 6-inch rifled breechloading naval guns, designed by the Royal Gun Factory in the 1880s following the first 6-inch breechloader, the relatively unsuccessful BL 6-inch 80-pounder gun designed by Elswick Ordnance. They were originally designed to use the old gunpowder propellants but from the mid-1890s onwards were adapted to use the new cordite propellant. They were superseded on new warships by the QF 6-inch gun from 1891.
The BL 10 inch guns Mks I, II, III, IV were British rifled breechloading 32-calibre naval and coast defence guns in service from 1885.
The RML 6.3-inch howitzer was a British rifled muzzle-loading "siege" or "position" howitzer/mortar proposed in 1874 and finally introduced in 1878 as a lighter version of the successful 8-inch howitzer that could be carried by the existing 40-pounder gun carriage.
The RML 64-pounder 64 cwt gun is a Rifled, Muzzle Loading (RML) naval, field or fortification artillery gun manufactured in England in the 19th century, which fired a projectile weighing approximately 64 pounds (29 kg). "64 cwt" refers to the gun's weight rounded up to differentiate it from other "64-pounder" guns.
The RML 10-inch guns Mk I – Mk II were large rifled muzzle-loading guns designed for British battleships and monitors in the 1860s to 1880s. They were also fitted to the Bouncer and Ant-class flat-iron gunboats. They were also used for fixed coastal defences around the United Kingdom and around the British Empire until the early years of the 20th century.
The RML 9-inch guns Mark I – Mark VI were large rifled muzzle-loading guns of the 1860s used as primary armament on smaller British ironclad battleships and secondary armament on larger battleships, and also ashore for coast defence. It should not be confused with the RML 9-inch Armstrong Gun, used by the Dutch navy, the Spanish Navy, and other navies.
The BL 6-inch 80-pounder gun Mk I was the first generation of British 6-inch breechloading naval gun after it switched from muzzle-loaders in 1880. They were originally designed to use the old gunpowder propellants.
The RML 12-inch 25-ton guns were large rifled muzzle-loading guns of mid-late 1800s used as primary armament on British ironclad turret battleships and coastal monitors, and also ashore for coast defence. They were the shorter and less powerful of the two 12-inch (305-mm) British RML guns, the other being the 35-ton gun.
RML 12-inch 35-ton guns were large rifled muzzle-loading guns used as primary armament on British battleships of the 1870s. They were the longer and more powerful of the two 12-inch British RML guns, the other being the 25-ton gun.
RML 11-inch 25-ton guns were large rifled muzzle-loading guns used as primary armament on British battleships and for coastal defence. They were effectively the same gun as the RML 12-inch 25-ton gun, bored to 11 inches instead of 12.
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.
The British RML 8-inch 9-ton guns Mark I – Mark III were medium rifled muzzle-loading guns used to arm smaller ironclad warships and coast defence batteries in the later 19th century.
Gas-checks were attachments to ammunition that revolutionised the performance of RML heavy guns. The first generation of RML heavy guns began entering service in about 1865. They all had Woolwich rifling and relied on studs on the projectiles for rotation. Gas-checks were first introduced in 1878 or soon after. They significantly reduced wear on the guns while also increasing their range and accuracy. Before long, studless ammunition was being manufactured for these guns, using gas-checks for projectile rotation. Gas-checks also facilitated a switch to the second generation of RML guns which used polygroove rifling and only supported studless ammunition.
An attached gas-check was a copper plate that was physically attached to the base of a studded projectile of rifled muzzle-loading ("RML") artillery, sealing the escape of gas between the projectile and the barrel.
A rotating gas-check was a copper plate that automatically attached itself to a specially-designed studless projectile of rifled muzzle-loading ("RML") artillery, sealing the escape of gas between the projectile and the barrel and imparting axial rotation to the projectile.
The RML 8-inch howitzer was a British Rifled, Muzzle Loading (RML) Howitzer manufactured in England in the 19th century, which fired a projectile weighing approximately 180 pounds (82 kg). It was used in siege batteries and in fortifications.
The RML 6.6 inch howitzer was a British Rifled, Muzzle Loading (RML) Howitzer manufactured in England in the 19th century, which fired a projectile weighing approximately 100 pounds (45 kg). It was used in siege batteries and in fortifications.
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