Aetna-class ironclad floating battery
Introduction HM Floating Battery ''Glatton'' in 1855The '''''Aetna''-class ironclad floating batteries''' were built during the Crimean War for the attack of Russian coastal fortifications.Britain and France each laid down five of these coastal attack vessels in 1854.The French used three of their batteries in 1855 against the defences at Kinburn on the Black Sea, where they were effective against Russian shore defences. The British plan to use theirs in the Baltic Sea against Kronstadt in 1856 was influential in causing the Russians to sue for peace. The development of such iron-armoured batteries was a step towards the development of ironclad warships. "These armoured batteries were among the most revolutionary ships ever built and provided British and French designers with the germ of the battleship. "One of the British batteries, ''Trusty'', was used for trials in 1861 with a prototype rotating turret, based on Captain Cowper Phipps Coles' designs.
Genesis Emperor Napoleon III initiated the design of armoured steam-powered batteries for the French Navy. 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. Trials at Vincennes showed that Lloyd's idea was more effective, so it was adopted.Napoleon wanted ten floating batteries built in time for the 1855 campaign, but as French industry could only build five in time, France's British allies were asked to build the other five. 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, so the British armoured batteries were not ordered until 4 October 1854.
Design These vessels were copies of the French ''Dévastation''-class batteries. The French batteries carried 16 guns, but had 24 gun ports. The British ''Aetna'' class were also intended to carry 16 guns, but the first four completed only carried 14 guns to reduce draught to . The Admiralty design drawing showed them with 32 gunports. These ports were very large  – .The wooden-hulled ''Aetna'' class had "straight vertical sides and a flat bottom with a very bluff bow and stern. Their armour plates, nominally 4 inches (102 mm), but in many cases were rolled  under thickness, were locked together with tongue and groove joints." The iron armour was supported by  oak sides. The wooden upper deck was  thick. There were two conning towers protected by  wrought iron plate.In October 1858, experimental 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 +Ships of the classNote that there is a typographical error on page 241, where it says that the ''Aetna'' was launched on 3 May 1854, which should read '''3 May 1855'''. Lyon & Winfield state that the armour thickness was 3.5–4.5 inches for the ''Aetna'' class, and 4.5 inches for ''Aetna'' (ii). The other sources referenced give the maximum hull thickness as 4 in. The details in Lyon & Winfield are within the 0.5 inch tolerance for rolled armour of the period.Ship(a) Hull builder(b) Main machinery manufacturersOrderedLaid downLaunchedCompletedInitial costTotalinitialcostHullMachinerytocompletefor sea '''''Aetna'' class'''  (i) (a) J Scott Russell, Millwall(b) J Scott Russell 4 Oct 1854 9 Oct 1854 3 May 1855 Never Never delivered, caught fire during construction  (a) CJ Mare & Co, Limehouse(b) Maudslay, Sons & Field  4 Oct 1854  9 Oct 1854 17 Apr 1855  4 Jul 1855 £43,799 £10,123  £7,468 £61,390  (a) CJ Mare & Co, Limehouse(b) Miller, Ravenshill & Co  4 Oct 1854  9 Oct 1854 17 Apr 1855 21 Jul 1855 £43,784 £10,343  £8,210 £62,337 '''Broad beam ''Aetna'' class'''  (a) R & H Green, Limehouse (no 314)(b) Miller, Ravenshill & Co  4 Oct 1854  9 Oct 1854 18 Apr 1855  3 Aug 1855 £43,479 £11,244  £5,858 £60,581  (a) R & H Green, Limehouse (no 315)(b) Miller, Ravenshill & Co  4 Oct 1854  9 Oct 1854  3 May 1855 13 Jun 1855 £43,491 £10,446 £10,004 £63,941 '''Lengthened ''Aetna'' class'''  (ii) (a) Chatham Dockyard(b) Maudslay, Sons & Field 16 Nov 1855 25 Nov 1855  5 Apr 1856 1866Harbour service £38,357 £11,000    £495 £49,852Admiralty 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 Armstrong 40-pounder BL in January 1859 and the 100-pounder BL in September 1859; contrary to expectations, hits on her armour from the 40-pounder and 100-pounder had no serious effect. She was used in trials with a prototype Coles turret in 1861 and in so doing became the first warship to be fitted with a turret. She was broken up by Castle at Charlton in 1864. ''Glatton'' was also broken up in 1864. ''Thunder'' was broken up at Chatham in June 1874.
Footnotes