List of breastwork monitors of the Royal Navy The breastwork monitor was developed during the 1860s by Sir Edward Reed , Chief Constructor of the Royal Navy , as an improvement of the basic monitor design developed by John Ericsson during the American Civil War . Reed gave these ships a superstructure to increase seaworthiness and raise the freeboard of the gun turret s so they could be worked in all weathers . The superstructure was armoured to protect the bases of the turrets , the funnels and the ventilator ducts in what he termed a breastwork . The ships were conceived as harbour defence ships with little need to leave port . This meant that they could dispense with the masts , sails and rigging needed to supplement their coal - fired steam engines over any distance . Reed took advantage of the lack of masts and designed the ships with one twin - gun turret at each end of the superstructure , each able to turn and fire in a 270° arc . These ships were described by Admiral George Alexander Ballard as being like " full - armoured knights riding on donkeys , easy to avoid but bad to close with " . Reed later developed the design into the , the first ocean - going turret ship s without masts , the direct ancestors of the pre - dreadnought battleship s and the dreadnought s . Reed designed the first ship ( HMVS " Cerberus " ) at the request of the Colony of Victoria ; the India Office then ordered another of the same design ( HMS " Magdala " ) as well as a less expensive version ( HMS " Abyssinia " ) . The four " Cyclops " - class ships , enlarged versions of " Cerberus " , were ordered in 1870 for local defence of English ports . HMS " Glatton " was derived from the design of the first breastwork monitors , but sacrificed the rear turret for thicker armour and larger guns with which to attack enemy ports . She was given a deep draught to improve her seaworthiness , but her low freeboard meant that she had very little ability to weather head seas . HMS " Hotspur " was similar in layout to " Glatton " , but she was given more freeboard by the addition of an unarmoured structure above her waterline armour belt . Designed as a ram , " Hotspur " was given a fixed turret with four gun ports as a rotating turret was not thought capable of withstanding the shock of impact . HMS " Rupert " was an enlarged version of " Hotspur " , but used a " Glatton " - type turret instead of the fixed turret and thicker armour than the older ship . The two " Conqueror " - class ships were enlarged versions of " Rupert " with heavier guns , thicker armour and a steel hull . With the exception of " Cerberus " , all of these ships were sold off for scrap during the first decade of the 20th century . " Cerberus " was sold in 1924 and used as a breakwater ; her wreck still exists off Half Moon Bay in Australia . " Cerberus " class . The two " Cerberus " - class ships were the first breastwork monitors to be built . " Cerberus " was ordered in 1866 by the Colony of Victoria to supplement the shore - based fortifications of Port Philip Bay and to defend the colony in the event of a Russian attack . The India Office ordered a sister ship to defend the approaches of Bombay . " Magdala " was rearmed with four breech - loading guns in 1892 while " Cerberus " had a number of small quick - firing gun s added to her superstructure for defence against torpedo boat s . Both ships were fitted with three temporary masts for their delivery voyages , although only " Cerberus " had her freeboard raised with the addition of temporary bulwarks . The ships spent the bulk of their service lives in reserve and rarely , if ever , left their home port . " Magdala " was sold in January 1903 , but " Cerberus " was hulked in 1900 and transferred to the Royal Australian Navy when it was formed in 1911 . She was renamed HMAS " Platypus II " in 1918 and sold in 1924 . Stripped of all salvageable material , she was scuttled in 1926 as a breakwater , and her remains are still visible today . HMS " Abyssinia " . HMS " Abyssinia " was a smaller and cheaper version of " Cerberus " designed by the Dudgeon shipyard when the India Office ran out of money after it ordered HMS " Magdala " . She was intended as a partner for the larger ship in the defence of Bombay and had the same armament but one less inch of armour , and she was one knot slower . The ship was rearmed with eight - inch breech - loading guns in 1892 before being sold for scrap in 1903 . HMS " Glatton " . The design of HMS " Glatton " was also derived from that of " Cerberus " , although she exchanged one turret for heavier guns and armour . She was given a deeper draught for better seakeeping abilities , but retained the low freeboard of the older ships to make her a smaller target , making it difficult to weather head seas in heavy weather . While nominally intended for coast defence , she was designed to attack the defences of deep - water ports like Brest and Cherbourg . " Glatton " was immediately assigned as tender to HMS " Excellent " upon completion and remained in Portsmouth for the bulk of her career . She participated in a gunnery trial in 1872 where HMS " Hotspur " fired on her turret at a range of . Neither of the shells that hit her turret penetrated although some rivets were dislodged . She was mobilised in 1878 for service with the Particular Service Squadron . In 1881 she received torpedo launchers as well as three small quick - firing guns for use against torpedo boats later in the decade . " Glatton " participated in the 1887 fleet manoeuvres , but she returned to reserve afterwards . She was sold in 1903 for breaking - up . HMS " Hotspur " . HMS " Hotspur " was inspired by a series of French coast - defence ships with the ram as their primary weapon . The layout of " Glatton " was modified with a fixed turret and her freeboard was increased over that of the older ship . The single 12 - inch gun was mounted on a turntable and could pivot at each gun port to maximise its arc of fire . It was nominally capable of firing forward , but this proved to damage the upper deck . " Hotspur " remained in reserve until 1876 after she was commissioned . She served with in the Sea of Marmara during the Russo - Turkish War of 1878 . " Hotspur " was reconstructed between 1881 and 1883 with the substitution of a new turret with two 12 - inch guns protected by the newly developed compound armour . The ship ' s breastwork was removed and replaced by side armour with transverse armoured bulkheads to form an armoured citadel . Her only active service thereafter was with the Particular Service Squadron of 1885 . She was guard ship at Holyhead until 1893 , then in reserve again until 1897 , and then relieved as guard ship at Bermuda . " Hotspur " remained there until sold in August 1904 . HMS " Rupert " . HMS " Rupert " was an enlarged version of " Hotspur " with a rotating turret , two smaller guns , and heavier armour . Her machinery was unsatisfactory and she could only make 12 knots rather than her designed . The ship was comprehensively reconstructed in 1891 – 93 when her old muzzle - loading guns were replaced by breech - loading guns , her machinery was replaced and a number of light quick - firing guns were added for torpedo boat defence . " Rupert " was sent to the Mediterranean after she was commissioned and served there from 1876 to 1880 . She was thereafter held in reserve at Portsmouth until being mobilised for the Particular Service Squadron during the Russian war scare from April to August 1885 . She was then assigned as guard ship at Hull until 1890 . After reconstruction she became guard ship at Pembroke Dock until 1895 , then at Gibraltar between 1895 and 1902 , and finally relieved " Hotspur " as guard ship at Bermuda until her sale in 1907 . " Cyclops " class . The " Cyclops " - class ships were slightly larger versions of " Cerberus " , and one knot faster , that were ordered to satisfy demands for local defence during the war scare of 1870 . While ostensibly for coast defence purposes , the Admiralty planned to use them to attack enemy ports and for operations in the shallow waters of the Baltic Sea . The pace of construction was initially quite fast , but the fitting - out work slowed drastically as the perceived threat of war declined . The ships spent most of their careers in reserve and were finally sold off in 1903 . " Conqueror " class . The " Conqueror " - class monitors were enlarged versions of HMS " Rupert " with improvements based on suggestions from one of " Rupert " s captains . The useless foremast was removed , and breech - loading guns and heavier compound armour were added . The rear superstructure was enlarged to better accommodate the crew and secondary armament . Six 14 - inch torpedo tube s were fitted above water . Both ships were assigned as tenders to the gunnery schools in Devonport and Portsmouth , although " Conqueror " did participate in Queen Victoria ' s Golden Jubilee Fleet review in July 1887 . Each ship remained in reserve except to participate in the annual fleet manoeuvres , although this ceased after 1894 . " Conqueror " was placed in reserve in 1902 and sold in April 1907 . " Hero " became a target ship in November 1907 and was sunk in February 1908 .