Creator Backlash: The book's author apparently hates the movie for being a 're-glorification' of submarine warfare and too pro-German and pro-war (unlike the clearly anti-war novel it was based on). Oh, and for the cast's constant overacting. This has led to a Death of the Author reaction from many of the film's fans; when he claims that the movie "re-glorifies" the u-boat corps, the most common reaction is "how in the world is any of thissupposed to be glorious?" - and if the author considers this a glorification of WWII Era submarine warfare, how miserable must it have been in actuality?
The actors were not allowed to expose themselves to sunlight a few months before shooting. Also, the scenes were more or less shot chronologically, so that their appearances would change realistically.
Jan Fedder, who played the injured sailor, really was injured when a special effect went wrong.
In the scene at La Rochelle harbor near the beginning, actor Otto Sander, playing a drunk Phillip Thomsen really was drunk. Originally another actor was slated to play that part, but he was fired before filming began...ironically enough, because he was too drunk all the time.
The cast were required to run drills of the emergency dive sequence, to ensure they were able to convincingly carry out the tasks the real crews had to perform during an emergency dive.
Throw It In: A fairly literal example. During one scene of the storm, the actor who played Pilgrim was swept off his feet by the rushing water and nearly thrown off the set. Bernd Tauber (Kriechbaum) realized he was suddenly missing and, with the cameras still rolling, helped him back to the hatch. Wolfgang Petersen did not realize it was an accident and initially wanted to do another take of this unscripted moment. The actor was actually injured and had to be partially rewritten so that Pilgrim spends a period of the cruise in bed.
In the middle of filming, the sailing shell of the U-96 used and the La Rochele U-boat pen were rented for several days' filming by the production crew of Raiders of the Lost Ark.