Comus - class corvette The " Comus " class was a class of Royal Navy steam corvette s , re - classified as third - class cruiser s in 1888 . All were built between 1878 and 1881 . The class exemplifies the transitional nature of the late Victorian navy . In design , materials , armament , and propulsion the class members resemble their wooden sailing antecedents , but blended with characteristics of the all - metal mastless steam cruisers which followed . Despite their qualities they had relatively short commissions , as they soon were rendered superfluous by the " flood of warships " built under the Naval Defence Act of 1889 . By the turn of the century all were in reserve , relegated to subsidiary duties , or being scrapped . Purpose . Great Britain had a worldwide empire , founded upon and sustained by seaborne commerce . To protect this trade and police its empire , Britain constructed many small and medium - sized cruisers , the latter typically armed with guns up to six inches in calibre . They were designed to serve long periods at sea , and therefore were equipped with sails . The nine " Comus " - class corvettes and their later derivatives — the two " Calypso " - class corvettes — were ships of this type . Design . Planning for six metal - hulled corvettes began in 1876 . These vessels , which became the " Comus " - class corvettes , were designed by Nathaniel Barnaby . Among the Royal Navy ’ s last sailing corvettes , they supplemented an extensive sail rig with powerful engines . Unlike their French rivals , which built fast steamers and needed neither long range nor a full rig of sail , the Royal Navy required their cruisers to be capable of long voyages away from coaling stations . Their ships therefore had a beamy hull to handle their sails , making them slower under steam than their French counterparts . The British vessels were similar in appearance and layout to the older wooden and composite - hulled small cruisers they were intended to replace , albeit larger and more powerfully armed . The vessels were among the first of the smaller cruisers to be given metal hulls ; with frames of iron or steel . The forefoot formed a ram forged from brass , a feature in vogue at the time . In common with older wooden vessels , their hulls had copper sheathing over timber beneath the waterline , but that timber simply encased the hull beneath , rather than being the hull itself . Had the iron hull itself been exposed to water , especially in the tropics , marine growth would quickly have fouled it , creating drag and significantly reducing speed . Copper had effective anti - fouling properties , but could not be affixed directly to iron as electrolytic corrosion would result . The metal hulls therefore were covered with wood , to which was attached the copper sheathing . The timber extended to the upper deck ; it was in two layers from the keel to 3 ft ( . 9 m ) above the water line , and one layer above . In an early case of a single builder taking responsibility for building an entire class the contracts for these first six vessels were all awarded to the John Elder & Company at Govan on the Clyde . They were all fitted with 3 - cylinder compound engines , with one high - pressure cylinder of 46 inches diameter being flanked by two low - pressure cylinders of 64 inches diameter . Two to three years later , the Admiralty ordered an additional three vessels to be built to the same design . However , construction of these was awarded to the Royal Dockyards at Chatham and Portsmouth . This second group differed by carrying a barque rig , compared with the ship rig of the first six ships . In addition , the compound engines in the new batch were of 4 - cylinder type , with two high - pressure cylinders of 36 inches diameter and two low - pressure cylinders of 64 inches diameter . In the " Comus " class , the bow above the waterline was nearly straight , in contrast to that of wooden sailing ships . The corvettes had stern galleries , similar to older frigates , but the ports were false , and there were no quarter galleries . Boats were carried both amidships and at the stern . The ships flew a barque or ship rig of sail on three masts , including studding sails on fore and mainmasts . The masts were stayed by shrouds which were anchored to chainplate s affixed to the inside of the gunwale s , rather than the exterior as in wooden sailing ships . Their sailing rigs enabled them to serve in areas where coaling stations were rare , and to rely on their sails for propulsion . The vessels had two complete decks , upper and lower , with partial decks at the forecastle and poop . The forecastle was used for the heads and working space for the cables . The poop deck contained cabins for the captain , first lieutenant , and navigating officer , with the double wheel sheltered under its forward end . Between these was the open quarterdeck on which the battery was located . Under the lower deck were spaces for water , provisions , coal , and magazines for shell and powder . Amidships were the engine and boiler rooms . These were covered by an armoured deck , 1 . 5 inches ( 38 mm ) thick and approximately 100 ft ( 30 m ) long . This armour was about 3 ft ( 90 cm ) below the lower deck , and the space between could be used for additional coal bunkerage . The machinery spaces were flanked by coal bunkers , affording the machinery and magazines some protection from the sides . The lower deck was used for berthing of the ship ' s company ; officers aft , warrant and petty officers forward , and ratings amidships , as was traditional . The tops of the coal bunkers , which projected above deck level , were used for seating at the mess tables . The living spaces were well - ventilated and an improvement over prior vessels . There were some refinements in the design among class members , and the armament in particular changed during their careers . In 1881 an enlarged version of the design was drawn up by Barnaby , with the hull being lengthened by another 10 ft . Two ships were ordered to this later design , which became the " Calypso " class . The " Comuses " and " Calypsos " were sometimes called the " C class " of corvettes , an informal term rather than an official designation . Armament . " Comus " was armed with two 7 - inch muzzle - loading rifles , eight 64 - pounder muzzle - loading rifles and four breech - loading 6 - inch 80 - pounder gun s , but the breech loaders proved unsatisfactory . The rest of the class were provided with four more 64 - pounders in place of the 6 - inch breech loaders , except for " Canada " and " Cordelia " , which exchanged all the muzzle loaders for ten of the new 6 - inch Mk II breech loading guns . A selection of light guns and Nordenfelt quick - firing guns , as well as a pair of torpedo carriages , were also carried . The large guns were in embrasures in the bulwarks of the upper deck ; this was a common ( and to some extent a differentiating ) feature of steam corvettes , as most frigates carried their main armament one deck lower . The details of the main armament varied between the vessels , and during their careers , as all were rearmed after their first commissions .