RML 10 inch 18 ton gun

The RML 10 inch guns Mk I - Mk II were large rifled muzzle-loading guns designed for British battleships and monitors. They were also fitted to the Bouncer-class flat-iron gunboats.

Design
The 10-inch gun was a standard "Woolwich" design (characterised by having a steel A tube with relatively few broad, rounded and shallow rifling grooves) developed in 1868, based on the successful Mk III 9-inch gun, itself based on the "Fraser" system. The Fraser system was an economy measure applied to the successful Armstrong design for heavy muzzle-loaders, which were expensive to produce. It retained the Armstrong steel barrel surrounded by wrought-iron coils under tension, but replaced the multiple thin wrought-iron coils shrunk around it by a single larger coil (10 inch Mark I) or 2 coils (Mark II); the trunnion ring was now welded to other coils; and it eliminated Armstrong's expensive forged breech-piece.

The gun was rifled with 7 grooves, increasing from 1 turn in 100 calibres to 1 in 40.

It was first used for the main armament on the central battery ironclad HMS Hercules, completed in late 1868.

A number of the Mk I guns on HMS Hercules and one of the two damaged guns in HMVS Cerberus suffered from cracked barrels. Presumably this is why only a few (at least 25) Mk I guns were made.

Ammunition
When the gun was first introduced in 1868, 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 70 pounds "P" (pebble) or 60 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 44 pounds "P" or 40 pounds R.L.G. gunpowder, as for these velocity was not as important.

Surviving examples

 * 4 guns submerged near the remains of HMVS Cerberus in Half Moon Bay, Victoria, Australia (3 x Mk I & 1 x Mk II)
 * Damaged Mk I gun No. 17 from HMVS Cerberus is on display at HMAS Cerberus Victoria, Australia
 * Mk II gun No. 67 at Southport Gates, Gibraltar
 * A Mk II gun at Parson's Lodge Battery, Gibraltar
 * Mk II No. 273 at Almeda Gardens, Gibraltar
 * Mk II guns Several guns at Fort St Catherine, St George's Island, Bermuda (at least three are Mk II guns)
 * A Mk II at the Citadel, Quebec City, Canada

One 10 inch Mk I Common Shell, one 10 inch Mk II Common Shell & one 10 inch Mk III Palliser Shot as part of the Victorian Navy display at the Geelong Maritime Museum, Australia. Details

Various other guns are mounted or unmounted in Bermuda, with some lying outside of Fort St Catherine, having been rolled out when made obsolete, and a number having been found buried in the moat of Fort Cunningham (the two mounted at Fort George are the RML 11 inch 25 ton gun). At least one has been erected on a display stand at Fort Hamilton, though the original mount is missing, and another at Alexandia Battery.