Pelorus class third class cruisers

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. The Pelorus and Pearl class cruisers were often referred to jointly as the “P” class, despite a number of significant differences in design.

The two classes demonstrated different approaches to the problem of producing fast but small cruisers. The Pearl class ships could reach 19kts, but only by pushing their engines from a normal draught rating of 4,000ihp up to 7,500ihp using forced draught. This big an increase in power and pressure put the boilers under a great deal of strain, and so the Pelorus class ships were made longer and narrower. This increased the speed they could achieve on the same level of power but made then poor seaboats. This was combined with the use of more powerful engines that could provide 5,000ihp at natural draught. The power with forced draught was limited to 7,000ihp, which required a much less damaging increase in engine pressure. Despite the 500ihp decrease in maximum power, the Pelorus class ships were 1kt faster than the Pearls.

The Medea class ships had been armed with six 6in guns, three on each side – one of the forecastle, one amidships on the upper deck and one on the poop deck. On the Pearl class the guns had been decreased in size to 4.7in (thus the third class designation), but increased in number to eight by adding a second amidships gun on each side. On the Pelorus class ships the number and location of the guns remained the same, but the size was decreased again, this time to 4in.  

The Pelorus class ships were used to experiment with four different types of watertube boilers. HMS Pactolus and HMS Pomone were given Blechynden boilers. These proved to be problematic and the ships were removed from active service - the Pomone was converted to act as a training ship in 1910 and the Pactolus became a submarine depot ship in 1912.

Thornycroft Water Tube Boiler, Paul Jones Class Destroyers
Thornycroft Water Tube Boiler, Paul Jones Class Destroyers

Pelorus herself was given Normand boilers. Pegasus and Pyramus were given Reed boilers (boiler problems would later play a part in the destruction of the Pegasus). The rest of the class used Thornycroft boilers. None of these boilers would be entirely satisfactory, and by the start of the First World War the surviving ships had lost up to 4kts from their forced draught speed.

HMS Pegasus was the only member of the class to be lost in battle. At the start of the First World War she was part of the Cape squadron, and was posted off the east coast of Africa. On 20 September, while her boilers were being repaired at Zanzibar, the German cruiser Königsberg attacked her, inflicting damage that caused her to capsize before she could be safely beached.

HMAS Pioneer was transferred to the Royal Australian Navy in 1912. At the start of the war she was posted to the Fremantle station, to protect the eastern end of the trade routes to Australia. She was then posted to East Africa, taking part in the blockade of the Rufiji delta and the final operations against the Königsberg, before being laid up in 1916.

HMS Pelorus began the war patrolling in the Bristol Channel, but by the end of 1914 she was part of the Gibraltar Patrol. She was converted to act as a depot ship during 1916.

HMS Proserpine began the war as the light cruiser attached to the Eighth Battle Squadron of the Channel Fleet, but was soon moved, first to Gibraltar, then to the Suez canal in November 1914, before reaching Mesopotamia in 1915, where she remained for the rest of the war.

HMS Psyche was part of the New Zealand Division in August 1914. In that role she escorted the expedition that captured Samoa at the end of the month, and then escorted the main New Zealand troop convoy on the first leg of its journey to Britain.

HMS Pyramus began the war as part of the New Zealand Division, performing the same duties as HMS Psyche. She was then posted to the east coast of Africa, where she took part in the blockade and destruction of the Königsberg in the Rufiji Delta. She spent the rest of the war on the East Indies Station.

Displacement (loaded)


Top Speed

18.5kts natural draft
20kts forced draft

Armour – deck


 - gunshields


 - conning tower



313ft 6in


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

Crew complement






Ships in class
at start of war

HMS Pegasus
HMS Pelorus
HMAS Pioneer
HMS Proserpine
HMS Psyche
HMS Pyramus

Harbour Service by 1914

HMS Pactolus
HMS Pomone

Sold before August

HMS Pandora
HMS Perseus
HMS Prometheus

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

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

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