"Hydra" was laid down at the yard of Lobnitz, Renfrew. As a result of savings raised during "Warship Week", she was adopted by Wellingborough Urban District Council in Northamptonshire on 14 March 1942. She was launched on 29 September 1942. "Hydra" joined the 18th Minesweeping Flotilla in the Rosyth Command on 20 February 1943 and was transferred in May 1943 to the Nore Command. She was variously employed on minesweeping in the North Sea in 1943 and on escort duty with Arctic convoys from 1943-1944, including the convoys JW 55B and JW 57 to Kola in 1943-44.