The four ships in this class came about when the contracted supplier of the main armament for the Greek battleship Salamis being built in Germany was unable to supply due to the British blockade.

The company – Bethlehem Steel in the United States – instead offered to sell the four 14 in (356 mm) twin gun turrets to the Royal Navy on 3 November 1914.

[1] The Royal Navy was using obsolete pre-dreadnought battleships for shore bombardment in support of the army in Belgium, and a design for a shallow-draught warship (known as "Monitors") suitable for shore-bombardment was quickly designed and built to use these turrets.

[2] The monitors had a box-like hull, with very bluff bow and stern, and were fitted with anti-torpedo bulges.

The design included a seaplane for spotting the guns, but it was found that land-based aircraft were more effective; as monitors, they would never operate in the open sea, and storing the seaplane on top of the turret meant it had to be removed to avoid damage, even if not required before the guns could fire.