Frigates are multipurpose early naval units that have light shore bombardment and anti-naval capabilities and also provide anti-aircraft fire. They also have sonar and radar and are important intelligence units. Certain factions versions have other abilities like the UEF frigate's jammer or the Aeon frigate's torpedo defense system, it should be noted that the Aeon version has two guns that can only both hit the same target if they are broadsides and lacks anti-aircraft abilities. These ships are even flimsier than cruisers, though, so they should be used for their supporting abilities later in the game, or to quickly and cheaply build a large navy.