Factual error: Frank, Archie and Snowy are all rural boys from New South Wales, but they all play Australian Rules football expertly. In 1915 Australian Rules was almost unknown outside of Melbourne. In a time before television or film they wouldn't even know what the ball looked like. In fact the game was only established in Sydney in the 1980s, and is still not terribly popular there. There is no way that three people from New South Wales would know how to play the game in 1915, let alone with such skill.
Revealing mistake: In one scene just before the attack on a big Hunter the young captain (Jürgen Prochnow) is sitting with his charts. Beside him he has got a glass of beer standing. The sub lurches heavily right and left in the hard weather, but the surface of the liquid stays the same.
Visible crew/equipment: When the woman in the opening credits is taking off her clothes, she is about to take a blue shirt from her bag, but decided against it. As she does, you can see a crew member aimlessly wandering around in the bushes behind her. (00:01:40)
Factual error: In the final football game scenes ( from about three-quarters of the way through the film or so) all the spectators are wearing 1970's clothes and have 1970's hairstyles.
Deliberate mistake: When "Henry Faber" discovers the phony airfield, several helicopters with Army markings are among the aircraft visible. Although the Army did use helicopters experimentally during WWII, those used bore no resemblance to those shown in the film.
Factual error: In the boat-stealing scene, when the machine gunner fires a burst of blanks out of the M60 at the Cajuns, the weapon functions perfectly. However, the muzzle is bare. When firing with blanks, weapons have to have metal pieces called blank adaptors screwed into the muzzle to keep enough gas inside the weapon to cycle the bolt. Without one, the M60 would fire one round and stop.