Who does Canada believe the parachute rigger tells his USAAF story too?
Steve MacKendrick, nicknamed "Canada" because he claims he is from there, volunteers in 1940 for the British military's parachute training facility. He obviously has a good deal more experience and leadership skills than he lets on. Canada tries to become better acquainted with a pretty parachute rigger named Penny Gardner. She is initially put off by his attitude, but they eventually start dating. Both Penny and his new commander, Major Snow, see potential (and a mystery that does not add up) in him, despite his strong efforts to avoid assuming any responsibility. Canada turns down Snow's offer to send him to officer school.
After completing parachute school, Canada's unit goes on a raid on the German radar station at Bruneval. An RAF radar expert, Flight Sergeant Box, accompanies the raiders to retrieve a key component to take back to Britain. The mission is a success, but Corporal Dawes, one of the men in Canada's outfit, hurts both his legs in the drop. 
Back in Britain, after visiting Dawes, Canada is recognised by an American airman. He tells Penny that he resigned his commission from the USAAF after ordering his best friend and co-pilot to parachute out of their bomber when an experimental rocket got stuck. His friend was killed when his parachute did not open properly. Canada blamed himself and refuses any responsibility that might endanger anyone's life. When Snow confronts Canada with what he has learned (from a security investigation that he has ordered), Canada wrongly assumes that Penny told what she learned, and he breaks up with her.
Major Snow