Factual error: Princess Isabella was a 13-year-old girl living in France when William Wallace was executed in 1305. She didn't marry Prince Edward until 1308, and the marriage took place in Boulogne, not London.
Factual error: When Lt. Lee shoots down the second Messerschmidt in Italy, you can see it is a twin engine plane.
Factual error: James Graham, 4th Marquess of Montrose, became 1st Duke of Montrose in 1707, six years before the film is set, although the film refers to him throughout as a Marquess.
Factual error: The German pilot held prisoner is wearing a watch that is not correct for the 1940s. His watch is a late 80s / early 90s style watch.