Gem class third class cruisers

The four Gem class cruisers were the biggest, best and last third class cruisers built for the Royal Navy. They were 50% bigger, 2kts faster and carried 50% more 4in guns than the previous Pelorus class of third class cruisers. The guns were evenly spread around the ship, with five on each side and one at each end.

With the increase in size came an increase in seaworthiness. It had originally been planned to build eight Gem class cruisers, but only four were built before the light cruiser went out of fashion in Britain. Lord Fisher, the new First Sea Lord, believed that the fleet needed battle cruisers and large destroyers, but nothing between. When light cruiser construction resumed in 1909 with the Bristol class of light cruisers, the new ships resembled enlarged Gems, especially in their original all 4in gun configuration.

Commodore Reginald Tyrwhitt (1870-1951)
Reginald Tyrwhitt

HMS Amethyst was the first British warship larger than a destroyer to use turbine engines. She was not completed until March 1905, by which time it had already been decided to use turbines in HMS Dreadnought. Fortunately the Amethyst lived up to expectations, with a top speed of 23.4kts, a knot faster than her sister ships. The turbines were more economical at 20 kts, but not at low power, and so she was given a second set of lower powered cruising turbines.

HMS Amethyst began the war as the flagship of Commodore Tyrwhitt at Harwich. She was then transferred to the Mediterranean, taking part in the naval campaign off the Dardanelles and the first part of the Gallipoli landings, before being sent to Italy in May 1915. Finally, from 1916 to 1918 was stationed on the east coast of South America.

HMS Diamond spend most of the war attached to battleships, first with the Channel Fleet and then from 1915-1918 with the Grand Fleet. In 1918 she was sent to the Mediterranean to serve as a Coastal Motor Boat carrier.

HMS Sapphire began the war attached to the Channel Fleet. During 1914 she served with the Southern Force and then with the Dover Patrol. From February-May 1915 she took part in the Dardanelles campaign, before being transferred to the Italian fleet. In 1916 she was transferred to the East Indies station, staying there to the end of the war.

HMS Topaze began the war with the 5th Battle Squadron of the Channel Fleet. From 1915 to 1917 she served with the Italian fleet in the Adriatic, before moving to the East Indies from 1917 to the end of the war.

Displacement (loaded)


Top Speed (design)

22.5kts (Amethyst)

Top Speed (trials)

23.4kits (Amethyst)

Armour – deck


 - gunshields


 - conning tower



373ft 9in


Twelve 4in quick firing guns
Eight 3pdr quick firing guns
Four machine guns
Two 18in above water torpedo tubes

Crew complement






Ships in class

HMS Amethyst
HMS Diamond
HMS Sapphire
HMS Topaze

Books on the First World War | Subject Index: First World War

How to cite this article: Rickard, J (13 November 2007), Gem class third class cruisers ,

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