RML 12 inch 25 ton gun

The RML 12 inch 25 ton guns were large rifled muzzle-loading guns 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.

Mark I
Four guns were first made in 1866 with a toughened mild steel tube surrounded by multiple wrought iron coils on the original Armstrong pattern.

Mark II
While strong, the multiple coils were considered too expensive for construction in quantity. From 1867 guns were built on the simplified and hence cheaper "Fraser" system involving fewer but larger coils similar to the 10-inch (254-mm) Mk II gun. The guns were not considered a success, with the rifling twist of 1 in 100 increasing to 1 in 50 considered insufficient for accuracy, and guns were retubed in 11-inch (279-mm) calibre when their bores wore out.

Naval service
Guns were mounted on :
 * HMS Captain (1869) : 4
 * HMS Monarch (1868) : 4
 * HMS Hotspur (1870) : 2
 * HMS Glatton (1871) : 2
 * HMS Belleisle (1876) : 4
 * HMS Orion (1879) : 4

Ammunition
The gun's primary projectile was 600 to 608-pound (272- to 275-kilogram) "Palliser" armour-piercing shot, fired with a "Battering charge" of 85 pounds (38.5 kilograms) of "P" (gunpowder) or 67 pounds (30.4 kilograms) "R.L.G." (gunpowder) for maximum velocity and hence penetrating power. Shrapnel and Common (exploding) shells weighed 497 pounds (225.5 kilograms) and were fired with a "Full charge" of 55 pounds (25 kilograms) "P" or 50 pounds (22.7 kilograms) "R.L.G.".

Surviving examples

 * At Drake's Island, Plymouth, UK