Meet an American captain on his first duty as a captain who knows every post of a submarine because he did each one of them. It is established from early on that the captain has been on some of the worst subs and knows literally everything on one.
The first mission for him as a captain is to rescue fellow sailors who were on an american submarine that got sunk from a Russian submarine.
Action is really intense very early on the movie. Diplomatic decisions are taken based on rapid military events. In the meantime a special-forces group is sent to Russian ground for a secret mission. The risks that are taken from both the USA government and our captain-protagonist are unbelievable.
Even if deep inside you want to believe that everything you see is possible (and most of them are) you can not expect everything to work. Sure there are moments that the movie uses to show that not everything goes according to plan and people do make mistakes. However this only adds to the disappointment of the choices made from every key character. Literally, every important decision made has a very tiny possibility to happen. Do not play the "this is a movie" card. The movie itself wants us to believe this is a story that could be reality somehow but you can not expect the result of battle in a war (and even worse your own life and your submarine) to be based on human faith.
The good news are that, if you do not overthink the possibilities, it is a really interesting movie. Sure, in the end you get to experience life lessons. You get absorbed to the plot and the transition between the government, the submarine and the special forces team. So, if you like long military movies, sit back and enjoy exceptionally good acting and a damn good story.
"Turner: You will be court martial-ed! Captain: It is my job to keep you alive long enough so you can testify."
"Turner: Did we just start a war?"