 One 30-second scene with all the principals running along the dock took an entire day to complete, with Cagney, Hale, and Tobias barely able to stand at the end of filming.With a Hollywood production in their midst, North Bay residents became such a persistent nuisance that the crew reverted to sending messages out of the location site by homing pigeons.The military background sequences were shot at RCAF Air Stations at Uplands, Trenton, Dartmouth, Jarvis, and Mountain View.