Factual error: The squadron flies B-25 bombers from a base in England, which was inaccurate - B-25s were flown from the Mediterranean and the South Pacific, but not England; mostly B-17s, B-24s and B-26s flew from England.
Factual error: At the Gestapo headquarters in Lyon Halloran and Sellinger come to a room with a sign "Dokument Zimmer". German is notorious for its enormous composite words, and the sign should have been "Dokumentenzimmer" or better "Dokumentenraum".
When Halloran sets the barn on fire to distract the Germans he lights up some straw with a match. All of a sudden you see flames flickering up at various places which could not be caused by the fire he made.