Built by the Teesside shipbuilder Richardson, Duck and Company from 1915–1916, Rosemary carried out minesweeping and anti submarine operations during the First World War.

[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.

[8] The ship was laid down by Richardson, Duck and Company as yard number 661,[9] and launched at their Thornaby-on-Tees shipyard on 22 November 1915,[10] and was accepted into service on 5 February 1916.

[8] After commissioning, Rosemary joined the 10th Sloop Flotilla, replacing sister ship Arabis, sunk in a clash with German torpedo boats on 10 February 1916.

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

[14] In February 1917, as a result of the German resumption of unrestricted submarine warfare, and the resulting heavy shipping losses in the Western Approaches, Rosemary, 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.

[16] By July that year, Rosemary had transferred to the Northern division of the Coast of Ireland Station, with headquarters at Buncrana.

[17] On 6 August 1917, Rosemary was part of the escort for Convoy HH.11, bound from Newport News to Glasgow and 81 nmi (150 km; 93 mi) west-northwest of Tory Island when the merchant ship Argalia was torpedoed and sunk by the German submarine U-94.

[19][20][21] By June 1918, Rosemary had transferred to the Northern Patrol,[22] and was listed as part of the 3rd Sloop Flotilla the next month.

[24] By December 1918, Rosemary had transferred to the 23rd Fleet Sweeping Flotilla, part of the Northern division of the Coast of Ireland Station, serving as Senior Officer's Ship.

[32] In February 1930, Rosemary was carrying out a fishery protection patrol off Murmansk when she was diverted to search for the trawler St. Louis, which had not been heard from since leaving Hull on 8 January bound for the fishing grounds off Bear Island.