A great simulation, but beware, you will spend alot of time just getting to the best parts of the game.
Formations in the game are basically easy ways to group units. This makes it nice to keep organized, the problem is that the formations are pre-built, so you can only customise after you build them. Although there are different levels so you can have a battalion of battleships (two battleships with little escort), or go up to fleet size, requiring between 20-30 ships depending on the formation. One nice feature is that in the fleet size formations automatically get tankers and transports, allowing your ships to go much father because the can be refueled on their journey and rearmed.
Bases serve as home for your ships. They can keep supplies and oil, and also serve as troop stations for moving personel around your nation. They can be upgraded with airports, flak guns, coastal artillery, and others that in the end will help influence a battle if you are attacked. Some defences require certain supplies to build them whereas other can just be built. A twist on the idea of resources is that you must build fleets of convoys to keep your bases replenished with oil, men, and other supplies. If you don't give them oil, you ships cannot refuel and will not get far from their port. The same goes for ammo. Convoys are formations you can build but are not offensive. They are escorted by destroyers but are not much against enemy forces.
The tatical part of the game is what makes it much more unique tham most RTS games. It not only allows you to see and order your ships around, but allows you to take control of your own aircraft, and fly them around to shoot down enemy planes or sink enemy ships. And to top it off, it allows you limited control of your ships anti-aircraft defences. Although it would have also been cool if they gave you controll of the main guns of your ships (Which they don't). There are also sea planes that can take off from you battleships and cruisers that have depth charges for enemy submarines.
Overall a great simulation best suited for those who want relativly realistic battles. Its only real shortcomings are no control of larger guns in tatical mode and a tough but realistic campaign (I have yet to win a war, he, he)