I can see it being based on a true story as written by tom cruise, with nothing comparable to the true story apart from the names.
I have never been a great fan of his, but really disliked him when he bought the story of Billy Fiske.
Billy was a young American who won winter Olympic gold and travelled the world before WW2. In his travels he encountered the nazis and didn't like what he saw. At the outbreak he travelled to Canada and onto the UK.
Billy joined the RAF and flew with the RAF. He flew in the Battle of Britain and on the 16th August during a dogfight his Hurricane was hit setting it alight. He managed to land back at Tangmere which was being heavily attacked by the Luftwaffe. Sadly due to burns received Billy Fiske died.
He is buried in Boxgrove cemetery, I first visited many years ago to thank him for coming over to help. An American giving up a wealthy lifestyle because of what he had seen to fight for what he felt was right.
When tom bought the rights the story of course changed, the RAF would be on their last legs, being decimated by the Luftwaffe. Churchill put's out a call to America and Billy Fiske would be part of a squadron that comes to the rescue.
When the story leaked out thankfully the American Air force Veterans were horrified and the film was dropped. Ever since I have thought tom cruise a complete arse.
Billy flew Hurricanes and not Spitfires as the film would have had. Billy was also not credited with shooting down any aircraft. I imagine tom would have had them dropping like flies.
All that is required for evil to prevail is for good men to do nothing. Billy did something and I am glad a little piece of England will be forever America.