She was slightly damaged by air attacks on 11 and 17 June near Malta after the Italians declared war on the Allies on 10 June. Together with her sisters , , the Australian destroyer , and the light cruisers and , she escorted Convoy AN.2 from Egypt to various ports in the Aegean Sea in late July. "Diamond" bombarded the Italian seaplane base at Bomba, Libya on 23 August. A week later she escorted four transports to Malta with "Dainty" and the destroyers and as part of Operation Hats. The ship escorted Convoy MB.8 during Operation Collar. After reaching Malta on 26 November, "Diamond" joined Force D and sailed to rendezvous with Force H, coming from Gibraltar. The next day, after the British forces had combined, they were spotted by the Italians and the inconclusive Battle of Cape Spartivento was fought.