Pearl, Pelorus and Gem class cruisers

HMS Philomel was the only Pearl class third class cruiser to see active service during the First World War
The Pelorus class third class cruisers were more heavily armed versions of the previous Pearl class of third class cruisers, themselves a more lightly armed version of the Medea class of second class cruisers.
HMS Pegasus was the only Pelorus class third class cruiser to be lost during the First World War, being sunk by the German cruiser Konigsberg on 20 September 1914
HMS Pelorus was the nameship of the Pelorus class of third class cruisers. At the start of the First World War she was on patrol in the Bristol Channel, but before the end of 1914 she had been sent to the Mediterraean, where she formed part of the Gibraltar Patrol
HMAS Pioneer was a Pelorus class light cruiser that was part of the Australian Fleet at the start of the First World War, serving off the west coast of Australia before taking part in the operations against the German cruiser Königsberg.
HMS Proserpine was a Pelorus class third class cruiser that served in the Channel, at Gibraltar, in the Suez Canal and in support of the British intervention in Mesopotamia during the First World War.
HMS Psyche was a Pelorus third class cruiser that spent the entire First World War serving in the Pacific.
HMS Pyramus was a Pelorus class third class cruiser that served in the Pacific, off the east coast of Africa, in the Persian Gulf and in the East Indies during the First World War, taking part in the operations that destroyed the German cruiser Königsberg in July 1915.
The four Gem class third class cruisers were the biggest, best and last third class cruisers built for the Royal Navy.
HMS Amethyst was a Gem class third class cruiser that began the First World War as the flagship of Commodore Tyrwhitt at Harwich before serving off the Dardanelles and on the east coast of South America
HMS Diamond was a Gem class third class cruiser that spent most of the First World War attached to the Grand Fleet.
HMS Sapphire was a Gem class third class cruiser that served with the Dover Patrol in 1914, at the Dardanelles in 1915 and on the East Indies station from 1916 to the end of the war.
HMS Topaze was a Gem class third class cruiser that served with the 5th Battle Squadron of the Channel Fleet in 1914-15, with the Italians in the Mediterranean in 1915-1917 and in the Red Sea from 1917 until the end of the war.