This Class of Light Cruiser was first included in the 1916 Emergency ~ Programme with an order for three ships. The 1917 Programme also included three of this type followed by another six the next year. However, only eight ships were completed as after the end of hostilities, four were cancelled.  The cancelled ships were to be named

HMS DAEDALUS        HMS DARING         HMS DRYAD         HMS DESPERATE.

Three ships of the later orders were towed to Royal Dockyards for completion

HMS DESPATCH   HMS DIOMEDE HMS DURBAN.

A proposal to convert HMS DIOMEDE for use as the Royal Yacht was made in 1922 but this was not approved, probably because of economic constraints.

"D" Class light cruisers displaced 14,850 tons with an overall length of 472.5 feet, a beam of 46.5 feet and a mean draught of 14.5 feet. They were larger than the earlier "C" ’ Class and had six 6" Gun mountings as main armament instead of five. Exceptionally HMS DIOMEDE had a prototype single 6" gun mounting fitted in "A"" position. It had an enclosed gunhouse, which enabled it to be used in adverse weather conditions. The additional 6" gun mounting in "D" Class Cruisers was fitted between the foremast and first funnel.. For anti - aircraft defence the Class origina1ly was provided with two 3" guns and some smaller weapons, but these were replaced during refits before 1939 by three 4" mountings. The additional 4" gun being sited aft. Four triple torpedo tube mountings were sited on the upper deck. The ship was fitted after build completion with a temporary revolving flying off platform for an aircraft, was fitted aft but this was removed during a later refit.

HMS DEHLI cost £840,182 and this figure is approximately the same for each ship.

The propellers driven by steam turbines with shaft horsepower of 40,000 provided a speed of 29 knots using oil fired boilers. Armour protection was provided for hull, steering and machinery compartments. Endurance at full speed was about 1,500 miles.

The original Compliment when used as Flagships for Destroyer Flotillas was 469 but was 450 in HMS DESPATCH and HMS Diomede which were not designed for that duty. After 1939, because of the addition of radar and more AA weapons the number of personnel increased.

After completion this Class of cruiser was deployed on foreign stations, two of them being attached to the New Zealand Division of the Royal Navy for over ten years.

Ships in this Class had all been relegated to Reserve Fleet duties by 1939 but they were brought forward for trade protection duties with Reserve personnel before the outbreak of war. Those deployed on Northern Patrol in the NW Approaches were found unsuitable for duty in the North Atlantic.  

Because of defects due to the weather conditions, "D" Class cruisers deployed for trade protection and interception on overseas stations had a far better record of availability.

After modern cruisers joined the Fleet, some "D" Class cruisers were used for training of personnel or as accommodation ships. However, two were present during the allied landings in Normandy.

HMS DRAGON which had been transferred to Poland and renamed ORP CONRAD. HMS DESPATCH which was specially altered for use as a HQ ship.

HMS DUNEDIN was the only ship of this Class to be lost and was sunk by a U Boat torpedo on 24th November 1941 off Pernambuco.

HMS DIOMEDE

"D" Class cruisers were ordered from Vickers at Barrow under an Emergency War Programme in March 1918 and laid down in June that year. She was launched on 29th April 1919 as the 3rd RN ship to carry the name, which was introduced in 1781. It had previously been used for a 4th Rate broken up in 1815. The ship was transferred for completion by HM Dockyard at Portsmouth as an economy measure and build was not completed until 24th February 1922.