This was the first Hollywood picture to be filmed entirely on location in Canada.
The air training school outdoor scenes were filmed at the Royal Canadian Air Force base Trenton, near Belleville, Ontario, where pilot trainees and staff served as extras in the film. The training aircraft used were North American Harvards, which were a Canadian version of the NA At-6 Texan trainer. The Silver trainers shown in flight, are North American NA-64 "Yale" trainers. They look very similar to the later North American AT-6 "Harvard", but have fixed landing gear with fairings, and the fuselage was fabric covered. 119 were delivered to the RCAF of which approximately 30 are still in existence.
The German fighter shown attacking the bomber group is a Hawker Hurricane in Luftwaffe markings.
The training facility depicted in the movie, "Uplands Air Base," exists near Ottawa, Canada. After WWII, it served as a jet squadron training base and later as a military helicopter transport facility. In 1995, the Canadian government shut down the base and it now serves as a reception area for VIPs.