The Topaze-class (or "Gem-class") cruisers were a class of third-class protected cruisers. They were the last class of protected cruiser built for the Royal Navy. Four ships were built and a further four ships of the class were cancelled before their keels were laid.
Sapphire, Topaze and Diamond were fitted with steam reciprocating engines and twin shafts developing about 10,000 indicated horsepower (7,460 kW), and generating a top speed of about 22 knots (40.7 km/h). Amethyst was fitted with steam turbines, making her the first ship larger than a destroyer to be so fitted. She developed 12,000 ihp and was capable of 23 knots, and although her maximum range at 10 knots was reduced, she benefited from greater efficiency at high speed, and compared with her sisters, she was able to travel 1,000 nautical miles further at 20 knots.