Reacting to rumors of large German cruisers armed with 6.9-inch (175 mm) guns for overseas service and the need to replace the elderly armoured cruisers deployed abroad, d'Eyncourt proposed an oil-fuelled and lightly armoured ship of 7,500 long tons (7,600 t) capable of 26 knots (48 km/h; 30 mph) and armed with 7.5-inch (191 mm) guns in turrets.

[1] Winston Churchill, First Lord of the Admiralty, objected to the size and cost of the ship and asked for a smaller and faster design armed with a mix of 6-inch (152 mm) and 7.5-inch guns, capable of 27.5 knots (50.9 km/h; 31.6 mph) using oil and a version of the new design using a mix of coal and oil as in the Birminghams in August 1913.

[1] In the early months of the First World War, German commerce-raiding warships and armed merchant cruisers seriously disrupted British seaborne trade as the need to form convoys or re-route ships to avoid areas that the raiders in which were operating seriously delayed sailings or lengthened voyages.

[2] On 12 October 1914 d'Eyncourt reiterated the arguments behind his "Atlantic Cruiser" proposal in a memo to the Board of Admiralty, adding that a fast mixed-fuel design with a large steaming radius would be very helpful for operations in remote areas where oil might not be available.

On 9 June the board met to consider specifications for a large light cruiser capable of hunting down commerce raiders anywhere in the world.

D'Eyncourt was subsequently requested to submit designs for a ship capable of 30 knots (56 km/h; 35 mph) with at least one-fifth power from coal-fired boilers and an armament of at least ten 6-inch guns.

The shape of the hull was based on that of the large light cruiser Furious with 5-foot (1.5 m) anti-torpedo bulges covering the engine and boiler rooms.

The fore and aft groups adopted a modern oil-fired design, but the four boilers in the middle compartment were coal-fired, so that cruising fuel could be easily obtained in foreign ports where oil was not available.

[8] The steam from the boilers was ducted into two funnels, the uptakes from the coal-fired central group being split and trunked in with those from the oil-fired ones fore and aft.

[10] In November 1917 the Admiralty decided to replace the coal-fired boilers in the three least-advanced ships with four oil-fired ones, but only Raleigh actually received this modification, which increased her power to 70,000 shp (52,000 kW) for a theoretical 31 knots (57 km/h; 36 mph).

[10] These three ships stowed 2,186 long tons (2,221 t) of oil[9] which was designed to give them the same range of 5,640 nautical miles (10,450 km; 6,490 mi) at 10 knots (19 km/h; 12 mph).

[6][13] To make room for her flight decks, HMS Vindictive was completed with just four guns, one forward, two in the wing positions, and one right aft.

It used data provided by the 15-foot (4.6 m) coincidence rangefinder in the pedestal-type gunnery director positioned under the spotting top at the head of the tripod mast.

[17] The Hawkins class were protected by a full-length waterline armoured belt of high-tensile steel (HTS) that covered most of the ships' sides.

The initial order had to be cancelled in April 1917 for lack of building facilities, so the Admiralty decided to convert Cavendish, already under construction, in June 1917.

[18] A port side gangway 8 feet (2.4 m) wide connected the landing and flying-off decks to allow aircraft with their wings folded to be wheeled from one to the other.

The first major refit to the class came in 1923, when Vindictive was converted back into a cruiser configuration - but the hangar beneath her bridge was retained, and in place of 'B' gun, she had a prototype aircraft catapult, enabling her to carry six Fairey IIID floatplanes on active service.

In 1925, it was suggested that Frobisher and Effingham could be rearmed to carry six 8-inch (203 mm) guns in the same modern twin-turrets used on the new County-class cruisers then building, giving ships of comparable firepower for a fraction of the cost, and a similar reconstruction of the partially coal-fired Hawkins could also be used to upgrade her boilers (Vindictive was excluded as her aircraft catapult was considered a valuable asset); but the proposal was rejected - the existing turret design produced for the new cruisers could not be used in the aft position on the older ships, their protection against long-range gunfire was weak, there were concerns with staying within the 10,000-ton weight limit, and the Admiralty reported that it would be difficult and costly to find substitutes to take over their duties while they were being rebuilt.

In 1930, another modernisation plan was proposed, which would re-arm the class with eight 6-inch (152 mm) guns in twin turrets, similar to the new Leander-class light cruiser.

A reworked superstructure provided cadet accommodation, while the empty aft boiler room became a laundry, and her fuel reserve dropped to 1,000 long tons (1,000 t).

The submerged torpedo tubes and the after boiler rooms were removed, but they were replaced with extra fuel storage, and after modifications to her remaining machinery, her total output was only slightly reduced to 61,000 shp (45,000 kW).

In the event, it was decided that she could be more usefully (and very quickly) refitted as a repair ship, eventually armed with six 4-inch (102 mm) guns, two quadruple pom-poms, and a number of 20-millimetre (0.8 in) Oerlikon autocannons.

Further wartime additions modified the anti-aircraft armament, generally strengthening the pom-pom arrangements and increasing the number of 20 mm guns.