 When Waldo is recounting his fight with Kessler at the start of the  movie, he mentions that his guns jammed and Kessler, seeing that he  was helpless, saluted then flew away. This actually happened to  Ernst Udet (on whom Kessler is based) when flying against the French  ace Georges Guynemer in 1917, only it was Udet (at that time  inexperienced) who had the jam and Guynemer (a high scoring ace) who  let him go.