Cyclops - class monitor The " Cyclops " class monitor was a group of four ironclad breastwork monitor s built for the Royal Navy during the 1870s . They were slightly modified versions of the s . The ships were ordered to satisfy demands for local defence during the war scare of 1870 , but the pace of construction slowed down tremendously as the perceived threat of war declined . The " Cyclops " - class monitors spent most of their careers in reserve and were finally sold off in 1903 . Design and description . The immediate reason why these ships were ordered was for local coast defence during the war scare during the Franco - Prussian War of 1870 , but they were chosen for several other reasons . They were small and cheap , and their shallow draft was thought to limit them to defensive operations , which appealed to economy and defence - minded Members of Parliament . The Admiralty , however , envisioned them attacking shallow - water ports that larger ironclads could not enter and operating in the shallow waters of the Baltic Sea . The ships used the basic design of the " Cerberus " - class breastwork monitors to reduce design and construction time . Their hulls were completed very quickly , but the pace of building reduced as the likelihood of their immediate use diminished . They were delivered to the Royal dockyards in 1872 and commissioned for fitting out , but a number of years elapsed before that process was completed as little sense of urgency remained . The ships had an length between perpendiculars of , a beam of , and a draught of at deep load . They displaced . Their crew consisted of 156 officers and men . The " Cyclops " - class ships and other ships of her type were described by Admiral George Alexander Ballard as being like " full - armoured knights riding on donkeys , easy to avoid but bad to close with . " While not unfit to face heavy weather their decks were frequently awash in even a moderate sea . Their accommodations were rated the worst in the fleet , referred to by ordinary seamen as " ratholes with tinned air " . Propulsion . The " Cyclops " - class ships had two steam engines , each driving a single propeller . " Cyclops " and " Hydra " had 4 - cylinder inverted compound steam engines made by John Elder that had a working pressure of . The engines produced a total of on sea trials which gave the ships a maximum speed around . The engines used by " Hecate " and " Gorgon " were built by Ravenhill and were simple horizontal 4 - cylinder direct acting steam engines . Their working pressure was and they produced a total of for about the same speed . The first pair of ships carried of coal while the second pair carried . This was enough to steam at . Armament . The ships mounted a pair of 10 - inch rifled muzzle - loading guns in each turret . The shell of the gun weighed while the gun itself weighed . The gun had a muzzle velocity of and was credited with the ability to penetrate a nominal of wrought iron armour at the muzzle . The guns could fire both solid shot and explosive shells . They were mounted on compound pivoting carriages that used hydraulic jacks to elevate and depress the guns . Armour . The " Cyclops " - class ships had a complete waterline belt of wrought iron that was thick amidships and thinned to at the ends . The superstructure and conning tower was fully armoured , the reason it was called a breastwork , with of wrought iron . The gun turret s had 10 inches on their faces and nine inches on the sides and rear . All of the vertical armour was backed by of teak . The decks were thick . Construction . Each of the ships was towed to Devonport from the builders in 1872 . They were commissioned and placed into reserve until finally completed . Refit . Although a recommendation had been made while the ships were still under construction to extend the superstructure out to the sides of the ship to improve their stability and habitability , this was not acted upon until they were refitted during the 1880s . This refit also strengthened the breastwork and upper decks , added another watertight bulkhead as well as a false keel . Four quick - firing 3 - pounder Hotchkiss guns were added on the breastwork for torpedo boat defence as well as five machine gun s and several searchlights . This increased their crew to approximately 191 men and added to their displacement . Service . HMS " Gorgon " was the first ship completed and she served as tender to HMS " Cambridge " , the gunnery school ship at Devonport , from 1874 to 1877 . All four ships were commissioned between April and August 1878 during the war scare during the Russo - Turkish War for service with Admiral Sir Cooper Key ' s Particular Service Squadron in Portland Harbour . She resumed her duties as tender to HMS " Cambridge " until she was refitted in 1888 – 89 . All four of the ships of the class participated in the annual fleet manoeuvers in 1887 , 1889 – 90 and 1892 ; in between times they were in Fleet Reserve . HMS " Gorgon " , like all of her sisters , was placed on the non - effective list in 1901 and sold in 1903 for £8 , 400 . HMS " Hydra " was the next ship to be completed . After her service with the Particular Service Squadron she was paid off at Sheerness and served as tender to HMS " Duncan " . The ship was refitted in 1888 – 89 and was in Fleet Reserve at Chatham until 1901 . HMS " Cyclops " , the lead ship of the class , was the third ship to be completed . She was placed in 1st Reserve after her completion . The ship was paid off at Chatham in August 1878 and refitted in 1887 – 89 . HMS " Hecate " was the fourth and final ship of the class to be completed . She paid off at Devonport after her service with the Particular Service Squadron . The ship was refitted in 1885 – 86 and was placed into reserve at Devonport afterwards .