Continuity mistake: In the scene towards the end of the film where we see Slade's body fall, it falls onto a submerged rock just below the surface of the water and there is a splash of water. In the next shot Tarzan looks down from the cliff above and Slade's body is on a large dry rock, a little distant from where the body originally fell.
Revealing mistake: When the UFO makes the huge flash that knocks everyone in the cemetery down, one of the police officers kicks a tombstone as he falls and it wobbles back and forth. (00:13:35)
Character mistake: In the scenes in San Diego, all the scenes outside the sub are taking place during daylight hours. Immediately after the crewman relays the message about the mysterious telegraph transmission, the scene shifts to the sub. The commander asks what time it is in Melbourne and is told it is 1500 hours (3PM). But if it were that time in Melbourne, it would be 10PM in San Diego, and thus not during daylight hours. (01:33:30 - 01:38:05)
Revealing mistake: During the chariot race, where the contestants are riding towards the screen, tyre tracks from the camera vehicle are clearly visible imprinted in the sand. (00:20:50)
Continuity mistake: After the boy's Noel-Coward-lookalike father says, 'Et les fruits?', goes into the kitchen, and disappears out of shot, watch the cat on top of the bookcase to the left of the door. Before the boy runs into shot, the cat suddenly changes position and a mysterious lens flare appears on the right of the screen, showing that it's actually two shots edited together.
Factual error: Towards the end when the cavalry uncovers the American flag, it has 50 stars.
Continuity mistake: The escape train stops at a station at which another train has been the site of a massacre. One of the victims of this massacre has his head leaning out of a railway carriage window. As Kenneth More and Lauren Bacall from the escape train walk about the station, he can be seen raising and then lowering his head again as he realises that the 'take' is not complete.
Continuity mistake: When Wilby goes into his bedroom, he takes out his PJ's from the bureau drawer, leaving the drawer open. He goes into the bathroom to put on the PJ's. When he comes out of the bathroom, the drawer in the bureau is closed.
Other mistake: Mick the orderly is Irish throughout the film, but when Nurse Dawson bumps into him and says, "You clumsy oaf," Mick's reply, "Look who's talking," is said in a London accent.
Plot hole: When the Allies blow up the airfield they pour gunfire from the backs of the trucks into the tents where the Japanese soldiers are eating. If you watch carefully you will see that the Allied guys in the truck nearest the screen are pouring lead through their comrades in the other truck. Another classic case of 'friendly fire'.
Factual error: The movie is set in Cardiff but the Transporter Bridge seen at the beginning of the film is really in Newport.
Continuity mistake: A sailor goes out on the luau covered deck to get his guitar, during an air raid. He lays down while a Zero strafes the deck hitting his guitar, which goes flying into the air toward the camera and lands about 10 feet from the sailor. In the next shot, the sailor kneels up and grabs his guitar which has appeared right next to him.