HMS Alyssum was an Arabis-class minesweeping sloop of the British Royal Navy which served during the First World War.

Alyssum was built in 1915 by Earle's Shipbuilding, and was used for minesweeping, escort and patrol duties in the North and Irish Seas.

[1][a] They were designed at the start of the First World War as relatively fast minesweepers that could also carry out various miscellaneous duties in support of the fleet such as acting as dispatch vessels or carrying out towing operations, but as the war continued and the threat from German submarines grew, became increasingly involved in anti-submarine duties.

[11] On 10 February a force of 25 German torpedo boats of the 2nd, 6th and 9th Torpedo-boat flotillas set out on a sortie into the North Sea.

[15] On the morning of 4 July 1916, the 10th Sloop Flotilla was carrying out sweeps of the routes to the German Bight used by the Grand Fleet.

[17] In February 1917, as a result of the German resumption of unrestricted submarine warfare, and the resulting heavy shipping losses in the Western Approaches, Alyssum, together with the rest of the 10th Sloop Flotilla, was transferred to Queenstown (now Cobh) in the South of Ireland, to be deployed on escort duties.

[20] On 18 March 1917, Alyssum, together with the sloop Myosotis was sweeping a minefield laid by the German submarine UC-66 off Galley Head, County Cork, when she struck a mine which exploded under the ship's bridge.