Plot hole: Towards the end of the movie, the characters use cell phones to determine whether or not the enemy is coming. However, throughout the whole movie, one of the girls has her cell phone, which never goes off even when the enemy is close.
Continuity mistake: At the end of the movie when the girl and guy are boarding the submarine, the camera switches to a view where you can see an apartment complex in the background. If you look towards the top you can see someone standing at the balcony and then they move off towards the balcony door. In the next shot the person is gone.