The RML 9-inch guns Mark I – Mark VI[note 1] 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.

Mark III in 1866–1867 eliminated the Armstrong forged breech piece and hence fully implemented the Fraser economy design.

These guns fired a special 360 lb (160 kg) armour-piercing shell to a range of 10,500 yd (9.6 km) using a propellant charge of 14 lb (6.4 kg) Cordite Mk I size 7½, remained in service through World War I and were not declared obsolete until 1922.

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.

(rifle large grain) gunpowder[10] was used for the Palliser projectile to achieve maximum velocity and hence penetrating capability.