Old school table top war games :)
If you are looking for a good computer game that accurately simulates modern naval combat, Harpoon is probably your best bet. There may be newer and better alternatives out there. Harpoon is a real time strategy game, which is probably the best way to really understand naval warfare. I do not really know of any turn-based, hex-based naval combat video games. This is sort of why we built this game engine. The great thing about Harpoon was the hyper realistic sensor models for things like radar, sonar, and electronic intelligence. We have tried to do a bit of that here, but in a turn based / hex based game engine.
Of course, there are lots of really good hex based/turn based modern naval warfare board games out there. One issue with board games is that you cannot really do a lot with sensors. This is where video games have the edge.
Trying to have the best of both worlds.