Navy Field is a WWII combat simulator. It gives you command of a single ship (The first is, I believe a Frigate) and sends you into combat to engage enemy ships. After a victory you are awarded a certain number of points which allows you to upgrade your equipment (and your crew- you have to hire crew) to outfit your ship with.
Once you have enough you can upgrade to differant classes of ships too, and from there the game evolves into a tech tree-based path, one will lead you to eventually command of a Battleship and the other will take you to command of an Aircraft Carrier.
Both the Japanese and Americans are playable, and I believe the British? As well as one other faction may be as well, though I stress that I don't know this for sure as it has been some time since I sat down and played the game.
It's online only (to my knowledge) sort of like Allegiance, but isn't very difficult to gain working knowledge of.
The reason I mentioned it was interesting earlier is because even though you can have seven or eight ships sitting in dry dock that you "own", you can only pick one to sail into battle with. Which means if you want to sink someones battleship and you're playing as a carrier, you're going to have to find a player with a carrier and team up with him to sink the enemy ship, which lends itself to some interesting cooperative play in the game.
Matches are found by selecting a "Tile" out in the ocean (there are many, many regions to choose from, with each having a "home port" so to speak. You set the desired number of players and spots fill up pretty quick. Due to the nature of the game there are always a large number of Frigates and Destroyers and then usually just one or two larger craft.
Combat is a little tricky, you steer your ship and having a target "Zone" that all of your shots will splash down in. I believe it is possible to set it to fire automatically but I always score better when I fire manually, myself.
It's pretty interesting, but like I said, last time I tried to pick it back up again a nasty bug in the installed locked up my system.