The rivets were coming off the internal fittings, not the pressure hull. And the four-rotor enigma was just a small mistake.
Oh, and
Crimson Tide is sooooo realistic, too!
http://us.imdb.com/title/tt0112740/goofs
Also, read these threads that appeared on sci.military.naval back when the movie came out.
http://tinyurl.com/h3utf
http://tinyurl.com/h95uy
Yup, no mistakes here!