Cast members such as R. Lee Ermey and Ray Wise were the only two actors with any talent and the lead "Jack Scalia" was really absolutely horrible. I think they cast him for his massive cleft chin. I was also annoyed with the stereotyping of the only black male on the set John Toles-Bey who must look at this movie and just wonder. Look him up sometime as he has done a lot of interesting movies.
But on this movie: The script as I said earlier was a rip-off of Aliens tweaked and turned into a submarine "thriller". It included such lines as "I got a bad feeling about this" and "Kill me" as one crew member is infected by one of the mutants and his belly starts doing the "alien hop" just before it pops out of his stomach. There is also a rip-off of the classic "get some!" via Bill Paxton. We also have a bunch of navy grunts running through caves with creepy crawlies popping out of walls. Even the explosions of the mutated creatures is very similar to the popping of aliens as they charge marines in the movie "Aliens". And the kicker is that some of the mutants spit acid (as opposed to having acid for blood). There are many more major examples. So if you want to see this script done well watch the first two classics Alien and Aliens (With Sigourney Weaver). You'll have a more enjoyable time.
The plot could have been interesting and done better if not for confusing sequences in the start of the movie and generally poor editing. Camera shots were pretty dull and honestly it wasn't very hard to stop watching it and walk around the room to get a snack or check email. Many of the interactions between characters made little or no sense and went nowhere more often than not. The whole command structure between crew and Capt. was poorly done. I'm not even sure if there are Captains in the military that have full control over nuclear subs. In general this just shows that there was little research done for background information to make the movie seem at least a little respectable and there are many other similar examples (like dive depth etc..).
If you like horrible movies or are a big fan of Alien and Aliens and want something to just laugh and shake your head at then this movie may be for you. As for me this one is going back on the shelf...permanently.