When the ship slips out of Sydney the captain orders full ahead as soon as the lines are dropped. This is an error in seamanship as the ship would run parallel to the dock and crash into whatever was in front of it. To properly get away from the dock, the stern first would be swung away from the dock, then go into reverse to enter the channel, then a forward command would be given, but not likely full steam ahead while still in the harbor.
Throughout the beginning of the movie, the Cruiser Rockhampton searches for the Ergenstrasse. The ship shown for the Rockhampton, is much smaller than a cruiser. Possibly a Frigate or Corvette.
When the ship is at Pom Pom Galli Capt. Erlich sends Heinz to the top of a mountain as a lookout. But according to Wikipedia, the actual Pom Pom Island has a maximum elevation of less than two meters.
When Wayne and Turner are on the mountain at Pom Pom Galli, you can see Wayne silently reciting Turner's lines, before it's his turn to reply.
The captain makes several references to his living space as quarters. The correct term for ships and boats is cabin. The term cabin is used in other scenes correctly.
All the "Germans" in the movie say their names like a bunch of Americans. For example, Wesser, Winkler, and Wentz are pronounced with the American "W" sound, rather than the correct Vesser, Vinkler, and Ventz. Also the ship's name "Ergenstrasse" is pronounced Ergenstrass in the movie, rather than Erganstrass-eh. Only one of the British naval officers pronounces the ship's name correctly. Likewise, the character Stemme is pronounced Stem in the movie, rather than Stem-eh.
Claude Akins is incorrectly listed in the opening credits as "Claude Akin".
Whe the ship first tries to sneak out of Sydney Harbor, in a shot of the engine room, the telegraph reads "voraus voll", or "ahead full", instead of the ordered "slow ahead".
The Ergenstrasse's pistols are Walther P-38s, which had only been adopted for military use the year before. It is unlikely that such weapons would be found on an old tramp steamer.
When David Farrar talks about Ehrlich's course options, he says they can rule out the vast Pacific to the west and the Indian Ocean to the east. Sailing from Sydney Australia, the Pacific would be to the East and the Indian Ocean to the West.
When Schleiter (James Arness) describes his method for chopping wood, he says, "... then I slice him port to starboard." In actuality, the slice he made was right to left, starboard to port.