"Simpson" was part of a support force formed on 18 March 1941, after the signature of the Lend-Lease Act, to protect convoys between America and Britain in the North Atlantic. After several months of coastal escort and patrol duties, she escorted two convoys from NS Argentia, Newfoundland, to a rendezvous with British escorts off Greenland between 30 June and 3 September 1941. On 24 September, off Iceland, she joined the first westbound convoy to be escorted by American warships and delivered it safely to Argentia on 4 October. After United States entry into the war in December, her convoy trips were extended to the British Isles, and she remained on transatlantic convoy duty until 28 April 1942, when she entered the Boston Navy Yard for overhaul.