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 cap badge worn by Captain Halliday of the RAMC is the Queen's crown version, which didn't come in to use until the 1950's. It is also made of brass, when it should be in a bronzed finish for officers.