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)
Other mistake: According to the plot, no life is possible in the Northern Hemisphere by the time the film is set. Yet, when the sailor who has been sent ashore to look around the San Diego refinery enters the premises (more precisely, when we see the smoking-prohibited sign on our right and his left) a bird can be seen flying in the upper left-hand corner of the screen.
Continuity mistake: In the part when the two American officers are looking around in Anchorage, USA, and come across the dead woman at the News Studios you can clearly see her blink 2 or 3 times as the camera pans out.
Other mistake: At the end of the movie when the family is on the bed, supposedly dead after ingesting suicide pills, you can see the little girl breathing as the camera pans away.
Continuity mistake: During the long shots in final scene as the submarine is leaving, the wind is so strong that the flag flies straight out behind the conning tower. During the close-ups of the crew, their shirts and hats show no wind at all.
Continuity mistake: Two scenes in the movie show a closeup of the tower on the submarine with a plexiglass shield in front of the actors. Both times you can make out the reflection of trees as the camera moves.