Factual error: The Merchant Navy rank insignia is very poorly researched. Each officer seems to have a different style of insignia, despite working for the same company and they incorrectly wear rank insignia on the shoulders of their blue uniforms as well as the cuffs. The main character, Junior Third Officer Mortimer, wears a bizarre mix of insignia, apparently consisting of a Royal Navy petty officer's sleeve badge, a Royal Navy chief petty officer's cuff buttons, and a rank badge of three inverted chevrons on his shoulder boards that doesn't seem to resemble anything from reality. In reality, he should simply wear a single cuff ring (or shoulder bar in white uniform).
Factual error: Although addressed as "Kapitänleutnant" in the film, Hartenstein had actually been promoted to Korvettenkapitän three months before the film is set. He is never seen wearing rank insignia, but he does correctly wear a Korvettenkapitän's oak leaves on his cap peak.