At first the 68-pounder's reliability and power meant that it was retained even on new warships such as HMS Warrior, but eventually new rifled muzzle loaders made all smoothbore muzzle-loading guns obsolete.

However, the large surplus stocks of 68-pounders were given new life when converted to take rifled projectiles; the cannon remained in service and was not declared obsolete until 1921.

Over 2000 were cast before 1861[8] and its exceptional durability, range and accuracy earned it a reputation as the finest smoothbore cannon ever made.

[10] Before it could be loaded the bore of the barrel was cleaned with a sponge, after which a propellant charge (gunpowder in a cloth bag) was rammed down into the breech.

[12] The gun crew still had to gauge the best length of fuse for the range they were firing – ideally the shell should explode just before hitting its target.

[4] It was fitted to numerous Royal Navy warships of different sizes such as HMS Queen, Odin, Victor Emmanuel, Sepoy and the Conqueror-class ships of the line.

[21] Along with 32-pounders and Lancaster guns they were taken from their ship mountings and dragged up to siege batteries by the Naval Brigade, from where they regularly bombarded Russian positions for the next year.

Originally it was intended to fit forty 68-pounders, primarily on one gun deck, but this specification changed during their building and they were finally equipped with twenty-six 68-pounders (13 on each side).

[22] Although the Armstrong guns represented a new direction in artillery, the breech loading mechanism meant that they were unable to withstand the explosion of a heavy cartridge.

[6] Ironically the Armstrong Guns were therefore incapable of penetrating the armour fitted to the Warrior-class ships, while the 68-pounder (with its high muzzle velocity) could.

[6][26] Eventually Captain William Palliser patented a method of boring out the gun barrel and inserting a wrought iron rifled liner.

[29] They were deployed as coast defence and garrison artillery around the British Empire and remained in service until eventually declared obsolete in 1921.