The unit was redesignated No.118 (Coast Artillery Cooperation) Squadron on 1 September 1939, activated for voluntary wartime service on 3 September, and moved to Saint John, New Brunswick on 28 October. 117 (Aux) Sqn from St-John N.B. was simultaneously absorbed into the unit along with personnel transferred in from No. 2 (AC) Sqn with their Atlas aircraft. These reinforcements formed a new A flight that would operate out of Halifax airport until 31 March 1940 when they moved to RCAF Station Dartmouth.