The regiment subsequently mobilized The Royal Rifles of Canada, CASF for active service on 24 May 1940. It was redesignated as the 1st Battalion, The Royal Rifles of Canada, CASF on 7 November 1940. The battalion served in Newfoundland on garrison duty from early November 1940 to August 1941. On 27 October 1941 it embarked for Hong Kong as a part of C Force, where it was destroyed while fighting in defence of the colony. The unit was reconstituted on 10 January 1942. It served in Canada in a home defence role as part of the Vancouver Defences of Pacific Command. On 2 January 1945 it embarked for Great Britain, where it was disbanded on 10 January 1945 to provide reinforcements to the Canadian army in the field.