In reserve at Boston and Charleston from 1 December 1919, "Cowell" put to sea for a training period out of Newport, Rhode Island, with a reserve organization from April through October 1921, returning to Charleston. On 27 June 1922, she was decommissioned at Philadelphia Navy Yard, where she lay until recommissioned 17 June 1940 for patrol duty in the Atlantic. She cruised along the United States East Coast on this duty until 18 September 1940 when she arrived at Halifax, Nova Scotia, there to be decommissioned 23 September 1940 and transferred to the Royal Navy the same day in the land bases for destroyers exchange.