Topaze-class cruiser

	HMS Amethyst
Class overview
Operators	Royal Navy
Preceded by	Pelorus class
Succeeded by	Town-class (1910) light cruiser
Subclasses	Amethyst
Built	1903–1905
In commission	1905–1921
Planned	8
Completed	4
Canceled	4
Scrapped	4
General characteristics
Class & type	Topaze-class protected cruiser
Displacement	3,000 long tons (3,000 t)
Length	360 ft (109.7 m) (p/p)
Beam	40 ft (12.2 m)
Draught	16 ft (4.9 m)
Installed power	10 water-tube boilers; 9,800–12,000 ihp (7,300–8,900 kW);
Propulsion	All except Amethyst:; 2 shafts, 2 triple-expansion steam engines; Amethyst:; 3 shafts, steam turbine set;
Speed	21–22 knots (39–41 km/h; 24–25 mph)
Complement	318
Armament	12 × 4 in (102 mm) guns; 8 × 3 pdr (47 mm (1.9 in)) guns; 2 × 18 in (450 mm) torpedo tubes;
Armour	Deck: 0.75–2 in (19.1–50.8 mm); Gun shields: 1 in (25 mm); Conning tower: 3 in (76 mm);

The Topaze-class cruisers (often referred to as the Gem class) were a quartet of third-class protected cruisers built for the Royal Navy in the first decade of the 20th century (four additional ships of the class were cancelled before their keels were laid).

As significant historical first, HMS Amethyst of this class was the first warship larger than a destroyer to be powered by turbine engines.

This class also embodied many historical lasts. Despite being units of the Edwardian-period Royal Navy, they represented the end of the Victorian-period lineage of protected cruisers in many ways. Amongst the many cruiser classes of the Royal Navy to have been rated as protected cruisers these were the last to be officially classified as such. They were the last British cruisers to feature the traditional arrangement of raised forecastle and poop connected by amidships bulwarks. They were also the last to be designed for propulsion by reciprocating steam engines, except for the aforementioned HMS Amethyst.

Perhaps most significantly of all, the Gems were the very last third-class protected cruisers to be so rated in the Royal Navy. The classes which followed were of similar type, and like the protected cruisers featured internal protective decks instead of armour belts, but were faster though weaker, and intended for a very specialised role, thus according them the new official type designation scout cruiser. When the later small turbine-propelled cruisers of the Arethusa class appeared (combining the features of scouts & second-class cruisers, to provide for greater utility & fighting power more in line with the Third Class), the new ships were designated from the outset as light armoured cruisers, thus dispensing with the third-class rating entirely.