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 turrets 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.[1] 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".[2] Reed later developed the design into the Devastation-class, the first ocean-going turret ships without masts, the direct ancestors of the pre-dreadnought battleships and the dreadnoughts.[3]
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.[4]
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.[5] 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.[6]
With the exception of Cerberus, all of these ships were sold off for scrap during the first decade of the 20th century.[7] Cerberus was sold in 1924 and used as a breakwater; her wreck still exists off Half Moon Bay in Australia.[8]