Destroyer
A medium-sized ship armed with long range stinger missiles that can target all but submarines. It is effective against vehicle and aircraft. It also has a depth charge launcher that shoots out two depth charges at submarines.
Cruiser
A large ship with twin cannons that fire excessively long ranges. The damage done by the cannons is deadly to infantry and structures, and has a good radius of splash damage.
Gunboat
Basic Allied ship that has a short range anti-tank cannon. It is effective against land vehicles and enemy ships. It also can shoot out single shots of depth charges at enemy subs. The gunboat is the fastest attack ship, and can outrun enemy torpedoes with ease.
Transport
Can carry up to five units, which can be a mix of either infantry or vehicles. This transport unit moves fast, but is unarmed and vulnerable to submarines.
Submarine
Stealth when not shooting, the Soviet submarine can traverse through naval channels undetected. It can fire a single torpedo a considerable range, and hit enemy naval units from outside their ranges. The sub is completely useless against any land or air units.
Missile Sub
Available in the Red Alert expansion, the missile sub is the counterpart to the Allied Cruiser. It can fire far and its missiles are effective against enemy structures.
Helicarrier
The Helicarrier is the rarest naval unit and is almost impossible to get. It is basically a ship that carries Longbows acting as a mobile helipad.