Alexander attempted to join the United States Army Air Corps but was rejected because he had only received a high school education and at least some college education was required for USAAF service. He joined the Royal Canadian Air Force in October 1940 to get involved in the war as a pilot as well as to avoid being drafted and sent to serve in the infantry. At the time, he had only 25 hours of flying experience, far below the normal requirements for the Royal Air Force (RAF). He earned his wings by 15 September 1941 and was assigned to the 133 Eagle Squadron in England. Nearly a year later, in August 1942, Alexander participated in Operation Jubilee, which he later called his "most memorable day in the RAF". In two missions as a part of this operation he shot down two German aircraft and damaged a third.