Reporting to the Portsmouth Navy Yard in Kittery, Maine, the trawler began conversion to war service as a minesweeper on 8 January.

The intention was to disguise the ship as a defenseless civilian vessel and, after luring an enemy submarine into close quarters on the surface, open fire with hidden guns and sink the unsuspecting U-boat.

As growing air and sea patrols had driven most U-boats away from the New England coast in May 1942, Captor had little chance to spot an enemy submarine and ended her wartime career without a single sighting.

With the decline in the U-boat threat to the east coast of the United States late in the war, Captor was decommissioned at Boston on 4 October 1944.

Stricken from the Naval Vessel Register on 14 October 1944, the trawler was transferred to the War Shipping Administration and sold on 21 February 1945.