The Humber-class monitors were three river monitorsunder construction for the Brazilian Navy in Britain in 1913, all three were taken over by the Royal Navy shortly before the outbreak of the First World War and were commissioned as small monitors, seeing extensive service during the war.
''Abercrombie''-class
The Abercrombie-class monitors came about when Bethlehem Steel in the United States, the contracted supplier of the main armament for the Greekbattleship being built in Germany, instead offered to sell the four 14"/45 caliber gun twin gun turrets to the Royal Navy on 3 November 1914, the ships were laid down and launched within six months, seeing service throughout the war.
''Lord Clive''-class
The Lord Clive-class monitors, sometimes referred to as the General Wolfe-class, were built to meet the need for more shore bombardment ships, using twin gun turrets taken from decommissioned Majestic-class pre-dreadnought battleships. Three of the ships, HMS General Wolfe, Lord Clive and Prince Eugene, were converted to take the BL 18 inch Mk I naval gun that had originally been allocated to.
''Marshal Ney''-class
The Marshal Ney-class monitors were built to use the two modern 15-inch turrets made available by the redesign of and as battlecruisers.
The M15-class monitors were fourteen ships ordered in March 1915, as part of the War Emergency Programme of ship construction, mounting 9.2 inch Mk VI gun turrets removed from the and the Mk X turrets held in stock for the and s.
''M29''-class
The M29-class monitors were five ships ordered in March 1915, as part of the War Emergency Programme of ship construction.
''Erebus''-class
The Erebus-class monitors were two ships mounting a single twin BL 15 inch Mk I naval gun turret. They saw active service in World War I off the Belgian coast, were placed in reserve between the wars then served in World War II, with Terrorbeing lost in 1941 and Erebus surviving to be scrapped in 1946.
''Roberts''-class
The Roberts-class monitors were two ships mounting a single twin BL 15 inch Mk I naval gun turret built during the Second World War, featuring shallow draught for operating inshore, broad beam to give stability and a high observation platform to observe fall of shot.