Deliberate mistake: Jimmy catches a fly in the air and puts it in his mouth. He then spits it out with great power. You then hear a "Bzzzzz." assuredly made by the fly. How can a fly flap its wings when spit out in that velocity? (00:48:30)
Deliberate mistake: In the scene near the end of the movie when Trigger is in the bilge trying to stop the air leak, the concussion of an artillery shell fired from the destroyer shakes some pipes loose. The mistake is that one of the flanges visible on a section of pipe has no bolt holes, making it impossible to join that pipe to anything.