The ship began a refit at Singapore on 7 August 1939 and she was transferred to the Mediterranean Fleet after it was completed in November. "Diamond" arrived at Malta on 19 December, but she was transferred to the South Atlantic Station the following month. She departed Malta on 8 January 1940, bound for Freetown where she joined the 20th Destroyer Division for escort duties. In April the ship returned to the Mediterranean where "Diamond" was assigned to the newly formed 10th Destroyer Flotilla after a short refit at Malta.