Steaming to Halifax, Nova Scotia, "McCook" arrived on 20 September 1940. Decommissioned on 24 September by the United States Navy, the destroyer was transferred to the United Kingdom on the same date, but due to manpower shortages in the Royal Navy, she was retransferred immediately to the Royal Canadian Navy and commissioned as HMCS "St. Croix" (I81). Following the Canadian practice of naming destroyers after Canadian rivers (but with deference to the U.S. origin), "St. Croix" was named after the St. Croix River forming the border between Maine and New Brunswick.