English: A model of the Dido Class Light Cruiser HMS Dido at the Glasgow Transport Museum, 2 March 2007.

Eleven Dido Class cruisers were launched in 1939-41 and completed in 1940-42 and five Modified Dido (or Bellona) Class vessels were launched in 1942 and completed in 1943-44. Although often described as AA cruisers, in fact they were conceived as trade protection cruisers to complement the larger 12x6” gunned 8,500 ton Crown Colony Class of fleet cruisers then being built at the same time. They were based on the 6x6” gunned 5,250 ton Arethusa Class of 1935-37 which had been regarded as too small to be regarded as effective fleet cruisers (although in fact they turned out to be very effective); instead of 6” guns, it was planned that the Didos would be armed with a new design of 5.25” guns and turret which, though optimised for surface use, could be used as an AA weapon and were therefore a dual purpose weapon. 5.25” was considered the largest practicable AA gun, although in service the turret’s training and elevating speed was somewhat slow in tracking fast moving aircraft. On the other hand, their air-burst was considered devastating.

The Didos emerged as a very innovative design with an unprecedented five twin turrets for its main armament with three stacked in the fore positions of A, B and C (and two in X & Y). Although this potentially raised the centre of gravity of the ship, this was counterbalanced by the first use of aluminium in considerable parts of the forward superstructure and bridge. The Didos measured 512 ft x 50.6 ft x 16.6 ft, with a displacement of 5,600 tons and a designed armament of 10x5.25”DP guns, 8x2 pdr AA pom poms guns (2x4), 8x0.5” mg AA and 8x18” TT (2x4). Their 62,000 shp turbines and 4 screws gave them a speed of 32 kts (although there is a claim that one ship reached 39 kts on trial!).

The outbreak of WWII led to a shortage of bauxite imports whilst what aluminium was produced was prioritised to aircraft production. This resulted to some ships having an all steel superstructure. This, together with delays building the complex 5.25” gun turrets, led to three ships being completed with only four 5.25” turrets and a 4” gun, including Dido although the fifth turret was later added. However, subsequently several ships had a 5.25” turret removed and replaced by various combinations of 1-3 twin/quadruple 40mm and/or 1-3 quadruple pom poms AA guns plus single/twin 20mm AA guns. Moreover, two ships were completed with a completely different main armament of 8x4.5” DP guns, which was at least a more effective AA weapon that the 5.25” guns if less hard-hitting in the surface role.

The Modified Dido or Bellona Class were redesigned with just four 5.25” turrets, upgraded and radar-guided, and a much lower superstructure to improve stability. Their role was also somewhat different to the main class in that they were intended to be escort ships for carrier task forces and also act as picket ships for amphibious operations. Their armament comprised 8x5.25” DP guns (2x4), 12x2 pdrs AA (3x4) guns, 12x20mm AA (6x2) guns and 6x21” TT (2x3).

Interestingly, although designed as trade protection cruisers or carrier escorts, in the Mediterranean the Didos and Bellonas were often used as fleet cruisers (with the Arethusas), participating, for example, in the Battle of Cape Matapan and the Second Battle of Sirte where they successfully held off larger and more powerful Italian cruisers. They were also at the Allied Invasion of North Africa, Salerno, D-Day and Okinawa. Their action-packed lives inevitably led to high losses, six being lost in WWII. So highly thought of was the class that, with the outbreak of the Korean war, there was a scheme to replace the 5.25” turrets with four or five automatic, radar-controlled, twin 3” AA turrets with an extremely high rate of fire but in the event it was found too difficult (and costly) to fit-in all the necessary equipment into a relatively small hull. The survivors were scrapped in 1955-68, although one sold to Pakistan survived until 1985.

HMS Dido herself was built by Cammell Laird, Belfast, being launched in 1939 and completed in 1940. She had a very active service in WWII (including the Second Battle of Sirte) and fired the last salvoes in the naval campaign in Europe in a shore bombardment in North Germany. The surrender of the German Kreigsmarine took place on her at Copenhagen. She then escorted the German cruisers Prinz Eugen and Nurnberg from Copenhagen to Wilhelmshaven. After the war she became the flagship of the Reserve Fleet and was scrapped in 1958.