There's really only so much you can do in a submarine movie: for example, there will always be a sequence involving silent running. Min wisely adds unexpected elements, and the eventual result owes as much to Nikita and Die Hard as anything else. Jung plays a sailor who shoots his commanding officer and is 'executed' by firing squad - only to wake up at a base for a secret Korean nuclear sub that doesn't officially exist, received from Russia to pay off a loan. Its crew are all known only by numbers, and he is now '431', with a second chance at life. But it all goes horribly wrong when 202 (Choi) kills the captain and takes over, intent on turning Japan into a radioactive wasteland. It's up to 431 to stop him.
After a slow start, once the mutiny takes place, the tension goes up to 'high', and pretty much stays there for the rest of the way. All thrillers need a nemesis, and Choi is excellent in that role, always giving the impression of being two seconds away from psychopathic violence, despite rarely raising his voice. A particularly nasty scene, involving the retrieval of a missile key, establishes quickly that this is a man who will be hard to deflect from his chosen path. The script elements tie together nicely with 431's background, and it all builds to an entirely non-Hollywood conclusion. An effective, efficient and claustrophobic piece of underwater work.