The Dido class consisted of sixteen light cruisers built for the Royal Navy during World War II.

During the war, the original 1939–42 ships required extensive refit work to increase electrical generating capacity for additional wartime systems (notably radar and gun direction equipment) and in the final Bellona, HMS Diadem, fully-electric turrets.

While some damage was experienced initially in extreme North Atlantic weather, changes to gun handling and drill partially mitigated the problems.

[3] The Bellonas were designed from the start with four radar-directed 5.25-inch gun turrets with full Remote Power Control and an expanded light anti-aircraft battery, substantially increasing their efficiency as AA platforms.

From the initial trials of the lead ship Bonaventure, the new light cruisers were considered a significant advancement and were surprisingly effective in later actions in the Mediterranean Sea, such as protecting convoys to Malta, seeing off far larger ships of the Italian Royal Navy.

[3] The 5.25-inch (133 mm) gun was primarily an anti-surface weapon but designed to fire the heaviest shell suitable for manual loading for use in anti-aircraft defence, and accounted for around 23 aircraft and deterred far more[citation needed].

Both the Didos and Bellonas were dogged by roller path jams in the rail track upon which the turret gunhouses rotated.

The survivor, name ship HMS Dido, was put into reserve in 1947 and decommissioned ten years later.

HMS Spartan was the only ship of the sub-class to be sunk, struck by a German Fritz X glide bomb while supporting the landings of the Battle of Anzio.

There was insufficient space and weight for the fire control and magazines of four or five modern twin 3-inch turrets, combined with the fact that the 5.25-inch shells had a much larger bursting charge than the smaller 4.5-inch guns in service postwar, making them more effective high-altitude AA weapons.

The class were intended to be armed with ten 5.25-inch (133 mm) guns in five twin turrets, which were of the same circular design as the secondary armament in the King George V-class battleships.

The 4.5-inch turret was better suited to the primary anti-aircraft role of the Dido class but the ammunition was considered too heavy for peacetime use.

The superstructure extended forward with more crew accommodation and radar rooms which allowed the two cruisers to operate as flagships.

The high rate of fire of the 4.5-inch turrets, together with simpler dual-purpose twin Director Control Tower (DCT),[a] meant that Scylla and Charybdis were arguably the only members of the Dido class that were true AA cruisers.

The production of the 5.25 turrets during the war and the turrets reconstruction, with remote power for faster elevation and training and better fire control was slow, difficult and expensive and largely limited to the cruisers rebuilt after severe action damage in the United States, Argonaut, Cleopatra and Phoebe.

Bellona, Black Prince and Royalist were lent to the Royal New Zealand Navy post-World War II.

In a long refit from October 1943 to July 1944, C turret was replaced by a quadruple 2-pounder pom-pom and two twin 20 mm were fitted.

Cleopatra was completed with two 2-pounder pom-poms in 1942 in lieu of the .5-inch machine guns but these were removed in the middle of the year and replaced by five 20 mm.

By April 1944 her light AA comprised three quadruple 2-pounder pom-poms, six twin power-operated 20 mm and five singles.

She was the only ship to receive an extensive postwar modernisation ordered for service in the RN but was later loaned to New Zealand.

However that would have required building new broad-beamed Didos because the magazines of the Royalist type could hold only enough 3 -inch ammunition for 3 minutes 20 seconds of continuous firing.

Royalist′s 5.25-inch armament was given some of the improvements of the final 5.25 inch mounts built for the battleship Vanguard but not the extra space or power ramming.

Babur became a cadet training ship in 1962 but was brought into use and her 5.25-inch guns were fired in the limited naval activities during the Indo-Pakistani War of 1965.