High Quality Content by WIKIPEDIA articles! HMS Diadem was a Dido-class light cruiser of the Bellona subgroup of the Royal Navy. She was a modified Dido design with only four turrets but improved AA armament - aka Dido Group 2. She was built by R. and W. Hawthorn, Leslie and Company, Limited (Hebburn-on-Tyne), UK), with the keel being laid down on 15 December 1939. She was launched on 21 August 1942, and commissioned 6 January 1944.