Upon commissioning "Diomede" joined the 5th Light Cruiser Squadron on the China Station in 1922. In 1925 she was transferred to the New Zealand Division of the Royal Navy at Devonport where she served until 1935, apart from a refit in 1929-1930. In 1931 she rendered assistance to the town of Napier, New Zealand after the devastating Hawkes Bay earthquake, supplying medical personnel, equipment, guards and firemen, along with her sister ship "Dunedin". Afterwards "Diomede" escorted the beach-damaged sloop to Auckland. The Executive officer at the time (1930-1933) was Commander, later Admiral Victor Crutchley, who was to later become entwined with the Pacific Campaign of World War II.