The Second World War broke out in September 1939. Initially the bomber force was used in a timid manner. Mahaddie was involved in a number of bombing missions which he termed "ineffective". Two young pilots Mahaddie met while at 77 Squadron who went on to have distinguished careers were Jimmy Marks and Leonard Cheshire. On the first night of the war his squadron was sent to drop leaflets over the Ruhr. Early wartime operations for No. 77 Squadron's Whitleys included reconnaissance flights, leaflet "raids" over Germany and attacks on easily reached coastal targets. On 1 April 1940 he received his commission as an officer. In May 1940 with the German invasion into France Mahaddie flew raids against the advancing German columns, and completed a total of 23 operations during the Dunkirk period between 10 May and 29 June. With the exception of the raid led by Marks against German forces near Rotterdam, the raids had little impact on events, and Mahaddie was disappointed in their effectiveness. The only other mission he felt had been effective early in the war was his group's raid against Stavanger, Norway, where they destroyed a number of hangars the Germans had been making use of at the airfield during the Norway campaign. As Mahaddie recalled, what the group lacked was the ability to navigate accurately enough to reach the target in strength, and the ability to carry the weight of bombs necessary to destroy the target once they got there.