She decommissioned and became a ship of the Royal Navy 23 October 1940 at Halifax, Nova Scotia as one of the destroyers transferred to England in exchange for bases in the West Indies.

Stanley was modified for long range trade convoy escort service by removal of the two forward boilers and substitution of additional fuel tanks.

Three of the original 4"/50 caliber guns and one of the triple torpedo tube mounts were removed to reduce topside weight for additional depth charge stowage and installation of Hedgehog anti-submarine mortar.

One of her first convoys took her to Freetown, Sierra Leone, escorting ships carrying troops and equipment for Commonwealth units in the Middle East.

On 17 December one of the escort carrier Audacity's aircraft sighted a submarine 22 miles (35 km) on the port beam of the convoy.