A mock-up of a conning tower was placed in a water tank at the Bavaria Studios in Munich for outdoor scenes not requiring a full view of the boat's exterior. When filming on the outdoor mockup or the conning tower, jets of cold water were hosed over the actors to simulate the breaking ocean waves. During the filming there was a scene where actor Jan Fedder (Pilgrim) fell off the bridge while the U-boat was surfaced. Fedder broke several ribs. This scene was not scripted and during the take one of the actors exclaims "" ("man overboard!") in order to draw attention to Fedder. Petersen, who at first did not realise that this was an accident, said "Good idea, Jan. We'll do that one more time!" However, since Fedder was genuinely injured and had to be hospitalised, this was the only take available and eventually Petersen kept this scene in the film. In this scene, the pained expression on Fedder's face is authentic and not acted. Petersen also had to rewrite Fedder's character for a portion of the film so that the character was portrayed as bedridden. For his scenes later in the film, Fedder had to be brought to and from set from the hospital since he suffered a concussion while filming his accident scene. Fedder eventually recovered enough and Pilgrim is seen on his feet from the scene when "U-96" abandons the British sailors. A half-sized full hull operating model was used for underwater shots and some surface running shots, in particular the meeting in stormy seas with another U-boat. The tank was also used for the shots of British sailors jumping from their ship; a small portion of the tanker hull was constructed for these shots.