The film was shot at Ibsley (now no longer in existence either as a base or a beacon, though you can see the remnants) which was in Hampshire, and in 1942 an active fighter station. The group of airmen listening to David Niven recounting the story of Mitchell were real RAF airmen. The filming did not stop for the war. If the bell went to scramble, filming would temporarily be halted while those airmen would run to their spitfires, go off and fight the war, before returning and carry on filming as though nothing had happened. At the end, Niven was so impressed with those heroes that he sent them off to The Savoy in London for the weekend, ringing the manager with instructions to give them whatever they wanted: women, drink, food, making sure the bill was sent direct to him. Difficult to imagine our pampered "stars" doing likewise these days! How do I know so much? One of those unsung heroes was my adored uncle Peter Howard-Williams, who had been in 19 Squadron flying out of Duxford during the Battle of Britain, but happened to be at Ibsley when the station was chosen for the film.