firing trials were undertaken against Meteor and one of the follow-on class of iron-hulled armoured batteries, . 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. Machinery The first four completed had two-cylinder diameter stroke horizontal single expansion engines of 150 nhp, which operated at . Although they were completed as single screw vessels, Meteor was altered to triple screw with wing-shafts; her trials with triple screw were 12 days after her trials with single screw. The most likely method of driving the wing shafts was a belt arrangement, which was common practice at the time. It is unclear whether any of the others were also altered to triple-screw. On trials with a single diameter, pitch screw, Meteor reached at 139 rpm with the safety valve set at 60 psi, and engine power was recorded as . On her trials fitted as triple screw, Meteor reached at 139 rpm. Engine power was recorded as . The two wing screws on this trial were diameter, pitch. The second Aetna had two-cylinder diameter stroke horizontal single expansion engines of 200 nhp. Her boilers were salvaged from the first Aetna. Building programme Admiralty records for Meteor, Thunder, Glatton and Trusty state that both the Mare and the Green yards were at Limehouse, other vessels built by Mare and by Green were built at Blackwall. It is possible that there is an error in the records, and they were actually built at Blackwall. Service The first Aetna was to have been launched on 5 May 1855, but caught fire on the building slip, and launched herself two days early. Her remains were broken up on the river-bank. Her replacement, the second Aetna was finished too late for the Crimean War, and was fitted for harbour service in 1866. She burnt out at Sheerness in 1873 and was broken up in 1874. Meteor and Glatton were ready in 1855 but reached the Black Sea too late for action. 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. Thunder and Trusty also took part in the review. Meteor was used in experimental firing trials in October 1858. She was broken up in 1861. Trusty was used in trials of the new