|Name||No||Yard No||Builder||Laid down||Launched||Comp||Fate|
|Topaze||P29, P2A, P1C||653||Laird, Birkenhead||14.8.1902||23.7.1903||11.1904||sold 9.1921|
|Amethyst||P00, P02||735||Armstrong, Elswick||7.1.1903||5.11.1903||17.3.1905||sold 10.1920|
|Diamond||N61, N33, 32, N70||654||Laird, Birkenhead||24.3.1903||6.1.1904||1.1905||sold 5.1921|
|Sapphire||N78, N89||775||Palmer, Jarrow||30.3.1903||17.3.1904||7.2.1905||sold 5.1921|
|Displacement normal, t||
|Displacement full, t|
109.7 pp 113.9 oa
|No of shafts||
Topaze, Diamond, Sapphire: 2
Topaze, Diamond: 2 4-cyl VTE, 10 Laird-Normand boilers
Amethyst: 3 Parsons steam turbines, 10 Yarrow boilers
Sapphire: 2 4-cyl VTE, 10 Reed boilers
|Power, h. p.||
Topaze, Diamond, Sapphire: forced draught: 9800
Amethyst: forced draught: 12000
|Max speed, kts||
Topaze, Diamond, Sapphire: forced draught: 21.7
Amethyst: forced draught: 22.5
Topaze, Diamond, Sapphire: 7000(10)
|Armour, mm||deck: 51 - 19, gunshields: 25, CT: 76|
12 x 1 - 102/40 QF Mk III, 8 x 1 - 47/40 3pdr Hotchkiss Mk I, 4 x 1 - 7.7/94, 2 - 450 TT (beam aw)
The Gem class were the last and largest of Britain's 3rd class cruisers. Topaze and Amethyst were ordered under the 1902/03 Programme and the other pair under the 1903/04 Programme, while a further four projected vessels were cancelled. In general they followed the style of earlier ships but were faster, carried more guns, were better protected and had improved seakeeping qualities. Two of the 102mm guns were fitted on the centreline of the forecastle and poop while the remainder were equally disposed along each side of the upper deck. The 47mm guns were mounted 4 on each side with 1 on the forecastle, 2 in the waist and 1 on the poop.
Amethyst was the first warship larger than a destroyer to be fitted with turbines, a modification decided upon so that she could be used for comparative trials with her TE-engined sisters. Turbines were more economic on fuel at high powers but less economic at low powers, and to compensate for this she was also fitted with cruising turbines which gave her an endurance of 5500nm at 10kts compared with 7000nm in her sisters; however, at 20kts her endurance was 3000nm compared with 2000nm in the others. On trials she achieved 23.4kts with 14,200shp and subsequently proved the most reliable ship of the class. All the remaining ships exceeded 22kts on trials, averaging 10,000ihp.
The protective deck was 25mm on the flat and 51mm on the slope amidships, reducing to 19mm flat and 25mm slope at the ends.
1918, Diamond: + 6 CMB-40 MTBs on davits
Diamond in 1918 was used as a 'CMB carrier' with 6 40ft CMBs carried in davits.
Many thanks to Wolfgang Stöhr for additional information on this page.