Factual error: The galley during the battle scene is rowed by slaves. Romans during this time period didn't use slaves to row their galleys. Rowers had to be able fight. If not, the Romans would be outnumbered 200 to 30 when they boarded the pirate ship as the pirates rowers would be able to fight.
Factual error: As Frederick is explaining to his guests how to use their .45 automatics, he fires one round at a near-by vase, shattering it. However, it leaves no bullet hole in the wall directly behind the vase.
Factual error: In the shot where the female band members run from their hotel (in Florida) to the beach, mountains can be seen in the background.
Factual error: Anne Frank received her diary on her birthday, and started writing on it 1 month before she went into hiding. In the movie however, she is presented with the diary on the first she arrives at the hiding place.
Suggested correction: Since this movie is based on actual events and not considered a documentary, then the film-makers are allowed to change things to their liking.
While I feel like this sort-of correction could apply to certain elements of movies based on true stories like dramatized scenes (since there has to be some condensation of time and some elements boosted for drama, which can be chalked up to filmmakers changing things), I think a film based on a true story contradicting a known hard fact like this should 100% count as a mistake. Otherwise, you could just as easily argue that any factual error in any film is invalid because the filmmakers are "allowed to change it."
Factual error: The movie is set in Cardiff but the Transporter Bridge seen at the beginning of the film is really in Newport.
Factual error: The USS Sawfish is supposedly a nuclear powered submarine, but the shots of her entering Williamstown show diesel exhaust coming from her. (Apparently they had to substitute an Australian diesel-electric submarine).
Factual error: In the scene where we see a DC-3 making a air drop over the jungles of "Burma" they fly over the ancient city of Sigiriya (a mountain fortress built around 473AD) which is actually in the country of Sri Lanka.
Factual error: The movie takes place "somewhere in the South Pacific, 1942", yet the transport plane taking LTJG Braden to Hawaii has post-war markings.
Factual error: When Mrs. Lane screams at the sight of the horse, on the back of Karen Steele you can see the outline of a modern bra under the shirt. (00:23:30)