RML 12.5-inch 38-ton gun

The gun originated from a desire for a longer gun than the existing RML 12-inch 35-ton gun. Experiments in 1874 with both and versions longer than the existing gun showed the calibre was more suitable, and further experiments showed a projectile of could be fired with a charge of of P2 gunpowder without undue strain. The same construction as in the existing 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. 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 ). 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 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. 38 ton gun shell - Hurst Castle.jpg|1 RML 12.5-inch Mk I shrapnel shell diagram.jpg|2 RML 12.5in Studded Palliser Shell Mk III with Attached Gas-Check Mk II.JPG|3 RML 12.5in Studded Common Shell with Attached Gas-Check Mk II.JPG|4 RML 12.5in Studded Shrapnel Shell with Attached Gas-check Mk II.JPG|5 RML 12.5in Case Shot Mk III.JPG|6 RML 12.5in Studless Palliser Shell Mk I with Automatic Gas-Check.JPG|7 RML 12.5in Studless Common Shell Mk I with Automatic Gas-Check.JPG|8 RML 12.5-inch Studless Shrapnel Shell.jpg|9 • 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. 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. == See also ==

• 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 ==