After completing contractors' trials in August 1939 she took up her war station in the North Sea as part of the 1st Minesweeping Flotilla.

In September she joined the flotilla, consisting of HMS Bramble, Hazard, Hebe, Sharpshooter, Speedy and Seagull at Scapa Flow.

The flotilla carried out these duties until November, when they were transferred to the Clyde following the sinking of the battleship HMS Royal Oak.

This kept them occupied until February 1941, when Britomart, Bramble, Hebe and Sharpshooter were transferred to Harwich to sweep convoy routes as part of the Nore Command.

Her repairs lasted from April to May, and on her return to service in June she joined the 3rd Escort Group with HMS Hazard and Bramble.

Britomart was nominated in August 1941 for detached service in North Russia, carrying out sweeping duties to ensure the safe passage of Russian convoys to and from Iceland.

Between October 1941 and January 1942 Britomart was engaged in sweeping operations in the Barents Sea, ensuring the safe movement of traffic in and out of the ports of Archangel and Murmansk.

She sailed for Reykjavík again in completion of these works and on 27 June 1942 joined convoy PQ 17 with HMS Salamander and Halcyon.

She was next deployed on 17 November with HMS Halcyon, Hazard, Salamander and Sharpshooter in escorting Convoy QP 15 through the Barents Sea.

On completion of the refit she was nominated to join the new 1st Minesweeping Flotilla, along with HMS Harrier, Gleaner, Halcyon, Hussar, Jason, Salamander, Seagull and Speedwell.

Throughout February and March 1944 they carried out their duties in the North Sea, and were subsequently nominated for minesweeping support during the planned allied landings in Normandy (Operation Neptune).

They sailed for Portsmouth in April 1944 and joined Force S. They were instructed to clear the approach channels to the beach head anchorage areas, and had three Motor Launches and four Isles class danlayers attached to the flotilla for these duties.

They were deployed on 8 June to begin widening the approach channels and carrying out defence patrols off the Eastern Task Force landing areas.

Salamander had her stern blown off and sustained heavy damage, while Jason was raked by cannon fire, killing and wounding several of her crew.