Factual error: The Tiger tanks portrayed in the movie are actually Soviet T-34s. You could tell by looking at their wheels. Real Tigers had interleaved wheels. These Tigers had the T-34 suspension. Obviously, Tigers are so rare (only one operational Tiger left) that another tank had to be substituted. But an excellent job was done to make the T-34s look like Tigers.
Factual error: When Pellew engages the first French warship, he gives the order to his helmsman, "Hard to Larboard". In the 18th century, helm orders were given in relation to the position of the tiller, rather than the rudder. A helmsman would push a tiller in the opposite direction he wanted the vessel to turn. This practice continued even when a ship was steered by a wheel, so the man at the wheel would have turned the wheel to starboard..except that he didn't.
Factual error: In the entire movie it's quite obvious Sean Penn has a digital watch on, even though the face is on the inside of his wrist it is occasionally visible, and the modern rubber watch band also gives it away, especially in his close-ups.
Factual error: When the Spanish sink the topsail schooner bringing supplies to Gibraltar, Captain Foster swims to a floating fighting top. The schooner actually had nothing more elaborate than a crosstrees on both masts.