The Aetna-class ironclad floating batteries were built during the Crimean War for the attack of Russian coastal fortifications.

"These armoured batteries were among the most revolutionary ships ever built and provided British and French designers with the germ of the battleship.

"[2] One of the British batteries, Trusty, was used for trials in 1861 with a prototype rotating turret, based on Captain Cowper Phipps Coles' designs.

The original idea was to protect the sides with boxes of cannonballs, but the British engineer Thomas Lloyd suggested using thick wrought iron plates instead.

[2] Unfortunately the First Lord, Sir James Graham, confused this concept with the unsuccessful iron-hulled frigates built in the late 1840s, and asked for further trials,[5] so the British armoured batteries were not ordered until 4 October 1854.

[2] The wooden-hulled Aetna class had "straight vertical sides and a flat bottom with a very bluff bow and stern.

[2] In October 1858, experimental firing trials were undertaken against Meteor and one of the follow-on class of iron-hulled armoured batteries, Erebus.

These demonstrated the importance of wooden backing for the armour, as Meteor put up far better resistance than Erebus, where the frames were displaced by concussion.

[6] The first four completed had two-cylinder 25.5 in (0.65 m) diameter 24 in (0.61 m) stroke horizontal single expansion engines of 150 nhp, which operated at 62 psi (430 kPa).

Both were laid up in theatre for the winter, and in the Spring, when peace was signed, they returned home for the great review of April 1856.