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[4] and Ant-classflat-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.
Design
Mk I & MK II gun barrels
The 10 in (25 cm) 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 in (23 cm) 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 in (25 cm) 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.[5]
The gun was rifled with 7 grooves, increasing from 1 turn in 100 calibres to 1 in 40.[2]
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.[6] Presumably this is why only a few (at least 25) Mk I guns were made.
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. Thus, any particular gun potentially operated with a mix of studded and studless ammunition.
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 lb (32 kg) "P" (pebble) or 60 lb (27 kg) "R.L.G." (rifle large grain) gunpowder[7] 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 lb (20 kg) "P" or 40 lb (18 kg) R.L.G. gunpowder,[7] as for these velocity was not as important.
Studded shell without gas-check. Southsea Castle UK
Studded shell without gas-check. Southsea Castle UK
Mk II guns Mark II guns numbers 156, 180 (dated 1871), 195, 221 and 224 at Fort St. Catherine, St George's Island, Bermuda (Guns were originally from Fort Albert)
One 10 in (25 cm) Mk I Common Shell, one 10 in (25 cm) Mk II Common Shell & one 10 in (25 cm) 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 (the guns actually mounted on display there were taken from other forts, notably Fort Albert), and a number having been found buried in the moat of Fort Cunningham (the two mounted at Fort George are the RML 11 in (28 cm) 25-ton gun). Three have been erected on concrete display stands at Fort Hamilton, though the original mounts are missing, and another at Alexandria Battery.
^Unit cost of £1,005 10 shillings 2 pence is quoted in "The British Navy" Volume II, 1882, by Sir Thomas Brassey. Page 38
^ abTreatise on Construction of Service Ordnance 1877, page 292
^1,364 feet/second firing 400-pound projectile with "Battering charge" of 70 pound "P" (gunpowder). Treatise on Construction of Service Ordnance 1877, page 348. 1,028 feet/second firing 410-pound common shell with gas-check with 44 pounds "P" (gunpowder). Victorian Navy Handbook 1887, page 211.
^Paloczi-Horvath, George (1996). From Monitor to Missile Boat Coast Defence Ships and Coastal Defence since 1860. Conway Maritime Press. p. 27. ISBN0-85177-650-7.
^Treatise on Construction of Service Ordnance 1877, page 92-93
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