HMS Orcadia was a Repeat that served in the Royal Navy during the First World War. The M class was an improvement on those of the preceding , capable of higher speed. Orcadia had a largely uneventful war. Joining the Fifteenth Destroyer Flotilla of the Grand Fleet in 1917, the ship was dispatched from the flotilla to the naval base Portsmouth, serving with the Local Defence Flotilla. The destroyer was allocated to the paravave depot, operating there into 1918. The paravane was a weapon used in anti-submarine warfare and minesweeping, although it lost favour with the Royal Navy as the war progressed. After the Armistice that ended the war, Orcadia remained with the Local Defence Flotilla at Portsmouth and was sold in 1921 to be broken up.
Orcadia was one of 16 Repeat s ordered by the British Admiralty in February 1915 as part of the Fourth War Programme soon after the start of the First World War. The M class was an improved version of the earlier , required to reach a higher speed in order to counter rumoured new German fast destroyers. The remit was to have a maximum speed of and, although ultimately the destroyers fell short of that ambition in service, the extra performance that was achieved was valued by the navy. It transpired that the German warships did not exist. The Repeat M class differed from the prewar vessels in having a raked stem and minor design improvements based on wartime experience.
The destroyer had a length of between perpendiculars and overall, with a beam of and draught of . Displacement was normal. Power was provided by three Yarrow boilers feeding Brown-Curtiss steam turbines rated at . The turbines drove three shafts and exhausted through three funnels. Design speed was , which the vessel exceeded on trials. A total of of oil was carried to give a design range of at . The ship had a complement of 80 officers and ratings.
Orcadia had a main armament consisting of three single QF Mk IV guns on the centreline, with one on the forecastle, one aft on a raised platform and one between the middle and aft funnels. Torpedo armament consisted of two twin torpedo tubes for torpedoes located aft of the funnels. Two single 1-pounder "pom-pom" anti-aircraft guns were carried. The anti-aircraft guns were later replaced by 2-pdr "pom-pom" guns and the destroyer was also fitted with racks and storage for depth charges. Initially, only two depth charges were carried but the number increased in service and by 1918, the vessel was carrying between 30 and 50 depth charges.
Orcadia was laid down by Fairfield at their shipyard in Govan on 24 June 1915 with yard number 518 at a cost of ã146,528 to build, launched on 26 July 1916 and completed on 29 September the same year, the first of the name in service with the Royal Navy. The vessel was deployed as part of the Grand Fleet, joining the Fifteenth Destroyer Flotilla. On 22 November, the flotilla took part in exercises north of the Shetland Islands under the dreadnought that also involved the majority of the First and Third Battle Squadrons.
At the start of the following year, Orcadia was detached from the flotilla to serve at Portsmouth naval base. There, the ship joined the Local Defence Flotilla and was allocated to the paravane depot. The paravane was a towed anti-submarine weapon that had been trialled by the Royal Navy on 27 May 1915 and was considered complementary to the depth charge. It was also used for minesweeping. However, the weapon had been increasingly ineffective, as the German submarines were able to dive below its maximum depth. Despite further work, the weapon increasingly became considered obsolete. Nonetheless, the destroyer remained at the paravane depot into the following year.
After the Armistice of 11 November 1918 that ended the war, the Royal Navy returned to a peacetime level of strength and both the number of ships and the amount of personnel in service needed to be reduced to save money. Orcadia initially remained with the Local Defence Flotilla at Portsmouth. However, this service did not last long. On 31 October 1921, the destroyer was retired and sold to W A T Burden to be broken up at Poole.