Prolly one of only 2 great games to ever come out of Korea (other is "Shattered Galaxy"), insanely fun and skill requisite navy combat game now being updated from old sprite engine to 3D.
Here is a video of beta of the new version, tonnes of videos of first game too, which basically plays the same.
http://www.youtube.com/watch?v=KQp16zv8eTM&feature=player_embedded#!
The game is both simple, and complex. You maneuver your ship around, and control your gunfire at same time. Aiming is actually pretty difficult since you manually adjust angles, so you need to know velocity and angles well, and calculate the relative movement/speed of both yourself and your target. There is shitloads of complexity though, since you completely customize your ship (within the space limits of the class), so you can up armour deck, or belt, or overgun it, turn it into an AA or torpoedo ship. Then you factor in subs and planes too. So a lot of statistical tinkering goes on, like in cRPG where small adjustments like trading from 6.5 inch cannons to add 2 inches of deck armour makes a big difference to how your ship plays.
As you play you level up, starting with just corvettes available, to destroyer, cruiser, etc. up to super battleships and fleet carriers. But even though smaller ships of course get obliterated by battleships (tho battleships usually avoid wasting their time on them, easy to miss a small fast ship, and they need to worry about other BBs), they are very fun to play and have useful roles. Destroyers hunt subs, and can shoot torpedoes which can ruin a larger ships' day, very fast and manueverable too so can dodge well. Subs can sneak up to capital ships and wreck them, cruisers can be decked out with AA and protect the fleet from planes, or can be outfitted with tonnes of torpedoes to spam them, or can be outfitted with guns to kill other cruisers, or smaller ships. A good heavy armoured cruiser can even tangle with weaker BB classes.
Just insanely fun and skill requisite game, this new one is supposed to be out in 2013, keep an eye out for it, heavily recommended.