For machinery the two monitors received diesel engines, which were then a novelty - the majority of ships being steam powered. The use of diesels meant that they had no need of boiler rooms which went well with a low draught, nor of large funnels which reduced the amount of superstructure. These engines were originally designed for much smaller freighters and therefore they proved particularly slow and unreliable.
The turret was on multi-sided barbette made of individual flat plates, cutting down on the build time. The 4-inch (102 mm) guns were disposed along her sides for protection from smaller vessels, the 3-inch (76 mm) guns being for anti-aircraft use.
Served with the Dover Monitor Squadron, after the war became a gunnery training ship. At the start of World War II she was considered for recommissioning but instead her turret was removed for a new monitor, Abercrombie and she became a headquarters ship. She was paid off and scrapped in 1946
After trials the turret was removed for Erebus and she was regunned with 6- and 4-inch (102 mm) guns and acted as a guardship until the end of the war. She later acted as a depot ship gaining onshore buildings, and was renamed Alaunia II and was only finally scrapped in 1957