HMS Erebus was a First World War monitor launched on 19 June 1916 and which served in both world wars. She and her sister ship Terror are known as the Erebus class. They were named after the two bomb vessels sent to investigate the Northwest Passage as part of Franklin's lost expedition (1845–1848), in which all 129 members eventually perished.
HMS Erebus in 1944
A monitor is a relatively small warship that is neither fast nor strongly armored but carries disproportionately large guns. They were used by some navies from the 1860s, during the First World War and with limited use in the Second World War.
USS Monitor, the first monitor (1861)
HMS Marshal Ney used a surplus 15-inch gun battleship turret.
Officers of a Union monitor, probably USS Sangamon, photographed during the American Civil War
Huáscar anchored in the harbour at Talcahuano