The regiment mobilized as The Toronto Scottish Regiment (Machine Gun), CASF for active service on 1 September 1939. It was redesignated as the 1st Battalion, The Toronto Scottish Regiment (Machine Gun), CASF on 7 November 1940; as the 2nd Infantry Division Support Battalion (The Toronto Scottish Regiment), CIC, CASF on 1 May 1943; and as the 1st Battalion, The Toronto Scottish Regiment (Machine Gun), CIC, CASF on 24 February 1944. On 7 December 1939, it embarked for Great Britain. The battalion took part in OPERATION JUBILEE, the raid on Dieppe, on 19 August 1942. It landed again in France on 6 and 7 July 1944, as part of the 2nd Infantry Division. The battalion continued to fight in North-West Europe until the end of the war. The overseas battalion disbanded on 31 December 1945