1:600 Dido class, as originally schemed, this time in "dual ship confusion" camouflage, with 5 twin 5.25" DP in the centreline, 2 octuple pom-poms and 4 quad 0.5" MGs controlled by a LA.DCT and a HA.DCT © Andrew Arthur

HMS Charybdis, 1:600, with new AA armament of 4 twin 4.5", and the 0.5" MGs suppressed and replaced by twin 20mm cannons. © Andrew Arthur

The "Dido" Class were designed primarily as fleet AA escorts, for which purpose they were fitted with a uniform armament of ten 5.25" guns of a new design. These were mounted in 5 dual-purpose turrets so that the ships were also capable of surface engagement. It was also required that they be "small cruisers" so that large numbers could be constructed to make up for the deficiency of cruisers in the Fleet.
Whilst an effective low-angle AA gun, the 5.25" was not so satisfactory in the high-angle role, but they could still throw up a fearsome flak barrage.
The hull and machinery were virtually the same as the earlier "Arethusa" Class, with such modifications as were required by the new armament.
A total of 16 ships were ordered, with the last 5 being completed to a revised design with straight funnels and masts and known as the Modified "Dido" Class.
Manufacture of the new 5.25" turret did not keep pace with the construction of the ships (the turrets were also required for the "King George V" Class battleships), and consequently Dido and Phoebe were completed without Q-turret and Bonaventure was completed without X-turret. All three mounted a single 4" HA/LA gun in place of the missing mounting, which was eventually fitted in the first two only - Bonaventure having been sunk.
No 5.25" guns at all were available for Charybdis and Scylla, who were completed with 4 twin 4.5" dual-purpose guns of the type fitted in the carrier Ark Royal. Neither ship ever received the designed armament, but in consequence, the heavy low-angle director could be removed, and the forward high-angle director lowered. There was no "Q" turret, and the lighter 4.5" mounts were placed in A & B and X & Y positions. Large forward deck-houses were built, easing accomodation problems. The 4.5" was a more satisfactory high-angle AA weapon, if less powerful.
The close-range armament of the ships was continually augmented during the war, the original quadruple 0.5" machine guns being replaced very early on. During 1943 Q-turret was removed from Argonaut, Cleopatra, Euryalus and Phoebe in order to reduce topweight. The turret was replaced by a quadruple 2pdr pom-pom in Argonaut and Euryalus and by a quadruple 40mm mount in the other two, who also had their original quadruple 2pdr replaced by quadruple 40mm. The final close-range armament varied from ship to ship, and comprised;

• 2~12 x 40mm
• 8~12 x 2pdr pom-poms
• 4~13 x 20mm.

The class served mainly in the Mediterranean, where they saw much front-line service including Malta convoys, the battles for Greece and Crete and the actions in the Gulf of Sirte. Best remembered are probably the three ships of the 15^th Cruiser Squadron (the "Fighting Fifteenth") - Cleopatra, Dido and Euryalus, under the command of Admiral Vian. In the latter years of the war most of the class transferred to the Home Fleet, but a few joined the Eastern and Pacific Fleets.

Pictures of Dido class anti-aircraft cruisers

HMS Argonaut, completed as originally designed. Note raked funnels and masts and high bridge to clear "Q" turret. From Steven Johnson's Cyberheritage

HMS Royalist, showing Bellona general arrangement. Note RDF fitted HA.DCTs, directed quad pom-poms, twin 30mm AA and new bridge profile. © Andrew Arthur

These ships were altered while under construction to incorporate lessons learned early in the war, and had vertical, instead of raked, funnels and masts. They also had a lower bridge as "C" turret was omitted and replaced by a third quadruple 2pdr pom-pom.
In 1943 Royalist was fitted out as a flagship for escort-carrier squadrons. Before being transferred to the Pacific, the ships were fitted with a number of 40mm Bofors.
Post-war all (except Spartan, a war loss) were loaned to or sold to Commonwealth navies. Royalist was extensively modernised from 1953 to 1956, being given an enclosed bridge, lattice masts, new search and fire-control radars, and a uniform anti-aircraft armament of 3 twin and two single 40mm.

Pictures of Bellona class anti-aircraft cruisers

HMS Black Prince. Note 5.25" turret, HA.DCT, straightened funnels and masts and sided pom-poms. From Steven Johnson's Cyberheritage