The later series cannon armed Spitfires used in the film were inaccurate, as the RAF had chiefly machine gun-armed Spitfire Mk I/IIs during the Battle of Britain. Limited number of early cannon-armed Spitfires Mk.IB served for brief time with No. 19 Squadron RAF, but these proved to be too unreliable and were soon withdrawn from active service. They also differed slightly from later cannon-armed Spitfire versions, which possessed both autocannons and machine guns, as their armament consisted of single 20 mm British Hispano cannon in each wing only. Ben Affleck's Spitfire is painted with the insignia "RF" – this is an insignia of No. 303 Polish Fighter Squadron.