After completing sea trials, "Nestor" was assigned to escort and patrol duties in the North Atlantic. During May, she was involved in the pursuit of the , but had diverted to Iceland for fuel when the Allied force encountered and sank the German ship. "Nestor" was transferred to the Mediterranean in July, and was involved in the Malta Convoys, then performed escort duties in the South Atlantic before returning to England for refit in October. The destroyer returned to service as a Malta Convoy escort in December. On 15 December, "Nestor" encountered the off Cape St. Vincent; the destroyer successfully hunted down and destroyed the submarine with depth charges.