Naval forces are normally large units with plenty of health that deal a lot of damage and have a good range. To offset these advantages, they are also relatively expensive.
The Illuminate lack a navy because many of their ground units possess the ability to hover.
Cybran naval units have the ability to grow legs via research. Once upgraded, they can go anywhere a land unit can, albeit very slowly. However, even the Salem Class Destroyer is much more powerful than a typical land unit and a group of naval units can be a devastating force. In addition, the Cybran navy benefits from range upgrades.
The UEF navy includes upgrades that focus on health and damage. Therefore, UEF ships are more battle-capable in a one-on-one fight with Cybran ships, provided they are in range to attack. However, UEF ships are stuck in the waters they are built in - there is no UEF upgrade for ship legs.
Naval ships are an excellent bombardment tool. They can attack a base from very far away, and if the opponent lacks radar intelligence, it can take some time to mount a counterattack. Cybran ships are all the more formidable once their range is upgraded. Even Salem Class Destroyers are able to attack Point Defenses from a safe distance, and Executioner Class Battleships end up with an incredible range of 179. Finally, once the land movement is researched, the Cybran player has a very powerful land army at his disposal. Provided the Cybran player keeps his ships near the shore as an escape route, he can slowly advance on an enemy base and destroy it from a distance.
Since naval ships have a considerable amount more health and damage potential, they are capable of destroying many land units on their own. An Illuminate player needs to send mass groups of land units to make a dent in a solid navy.
using their upgraded radar/sonar a submarine can effectively become a mobile, difficult to find, radar station, and even completely deny access to the ocean. this is especially punishing to Cybrans as they have no effective anti-sub constructed on land, whereas the UEF has torpedo bombers and the Illuminate have torpedo tanks and Wilfindjas, all of which can not be touched by torpedoes.
If an opponent's base is on the shore, Navy units, with particular respect to the UEF Navy due to its defensive and offensive upgrades, are excellent ACU killers. A squadron of Poseidons have enough firepower to kill an ACU in short order, while the Mastadons have the range to ensure the enemy Commander will need to retreat a long way to be free of incoming fire, or effectively hunker, and both have defense against tactical missiles