At the 45 minute mark of the movie, an African American naval officer on the Command deck, bearing rank insignia of Commander is giving out orders to his junior officers., who are also African American of various ranks. Fact is that the highest rank given to an African American naval officer in WW2 was Warrant Officer, and were prohibited from commanding white naval personnel, and there was no "black only" US naval vessel in WW2 or in history ever..
The American destroyer, attacks and sinks a U-boat with the Hedgehog which detonates in the water like a depth charge. In reality, Hedghog had a contact fuse which would only detonate if it hit the submarine.
In the early part of the movie, a German submarine is seen heading nose down sinking after a collision. In spite of a nose dive, crew walk easily along obvious horizontal floors. The captain calls "abandon ship" while the submarine continues down in to the deep. It would be impossible for the crew to escape a submarine in a deep dive.
Reality is that USA flag had only 48 stars in WW2, but all flags shown in this movie show the current 50.
Frequently during the movie, a German submarine is seen with 3 propellers. In reality, there were no 3 propeller submarines of any country in WW2. There was only one, 2 propeller German submarine ever put into service in in WW2, being the U-1225.
At the 30 minute mark, a close up is shown of the radio on board the German submarine, apart from all knobs and dials labeled in English, the specification plate can be seen which reads , "E.H. Scott Radio Laboratories Inc". (Obviously not German). And as the operator flicks the switch on to allegedly send the audio to speakers throughout the submarine, the power switch in the top left corner is still in the "off" position.
Throughout the movie, during the internal submarine scenes, labels on controls can be seen in English and not in German. Of the differing submarines, all have identical instruments and design in control rooms showing all were filmed in the same submarine or set.
Onboard the US Navy Ship's bridge: Obvious Plexiglas panels cover all the equipment consoles and switches. Revealing this set to be a Stationary Museum rather than an operational Naval vessel.
The aforementioned comment about the pistols being Walther PP's is incorrect. The pistols used were Mauser HSc's which were issued to Kriegsmarine and proof marked with an eagle over M.
St 55 minutes mark, the German U-boat captain drinks coffee from a USNavy issued coffee mug (the Watchman's mug).