Factual error: After the soldiers' initial disembarkment they are shown crouching in groups near the shore and later running towards the bunkers. Unlike the movie shows, anything even as simple as crouching behind the tank traps, let alone actually standing up and running, was impossible at Dog Green Sector and indeed for anyone when pinned down by a machine gun from a high far-away position. In the real-life landing at Dog Green within 7-10 minutes all the officers of the landing company were dead and the survivors inert. They could do nothing except throw away all their equipment and slowly crawl up the beach, shielded from bullets by the incoming tide and dead bodies. 1 hour 40 minutes after landing twelve (known) survivors made it to the base of the cliffs. Only 2 had enough strength left to go on and fight with another group. (The second wave, apart from one boat which was almost entirely killed, opted to land elsewhere when they saw the fate of the first wave.) In this way the movie rather poorly represents what it meant to make a properly opposed landing on D-Day - although whether this is justified or not is another matter. (00:07:00 - 00:07:40)
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.