On the outbreak of the Second World War, "Westcott" was still allocated to the Fourth Submarine Flotilla, and was having her armament restored to suit her for full operational service. In January 1940, "Westcott" was assigned to the Mediterranean Fleet, reaching Malta on 14 February. In April 1940, she was recalled to British waters, reaching Devonport on 19 April. She was then assigned to operations off Norway as a response to the German invasion, taking part in the evacuation of British troops from Åndalsnes on the night of 30 April/1 May, and continuing to operate off Norway for the rest of the month. In early June 1940 "Westcott" took part in the escort of a convoy (including the liners , , , and ) carrying Australian troops to the United Kingdom, on the leg from Gibraltar to Britain. "Westcott" then took part in Operation Ariel, the evacuation from ports in Western France of Allied troops who had remained in France following the evacuations from Dunkirk and Le Havre. "Westcott" was sent to Brest, but collided with the coaster "Nyroca" on 17 June, with both ships returning to the United Kingdom empty.