Commissioned at Toronto on October 14, 1941, Thunder arrived at Halifax October 30. After working up, she joined Sydney Force, but in January, 1942, was transferred to WLEF and subsequently to Halifax Local Defence Force, Shelburne Force, Halifax Force, and back to Sydney Force. She sailed with Bayfield, Georgian and Mulgrave from Halifax on February 18, 1944, for Plymouth via the Azores. Arriving on March 13th she was allocated to the 32nd Minesweeping Flotilla as Senior Officer's ship but was later transferred to the 4th Flotilla, and was present on D-Day. Thunder returned to Canada in August, 1944, to refit at Sydney but was back at Plymouth in late November assigned to the 31st Flotilla. In May, 1945, in the Bay of Biscay, she accepted the surrender of the German auxiliary minesweeper FGi 07. She sailed for Canada in September 1945, to be paid off on October 4 at Halifax, and was broken up at Sorel in 1947.