The United Systems Navy (USN) or United Systems Starfleet (USSF, it's a common dilemma because official sources uses both names and acronyms), is the military branch of the United Systems that manage the fleets of starships.
Currently, in 2090, the Starfleet is based on the First Fleet, composed by nearly 40 starships with different roles and purposes. Every ships of the navy is attached to a specific squadron or group, and its commonly commanded by an officer graduated at one of the Starfleet Academies that are present in most of the human colonies.
The main purpose of the Starfleet is to monitor and patrol the colonized space, providing protection to colonies for a possible outside menace. At the current time, no real engagements were performed, so the real value of the Starfleet is yet to prove.
The common classes of starships are:
Frigates
Small vessels that usually perform scouting tasks and intra-systems patrols.
Destroyers
The bulk of the navy, these are starship able to perform different tasks and actions, from scouting and patrol, to fleet escort operations, through combat actions and firepower support. They are typically armed with small fast missiles and their are always part of a squadron composed at least by another starship of this class.
Cruisers
Cruisers are relatively big starships, usually two times bigger than a destroyer, able to perform even solitary combat operations and sustain prolonged engagements. They are armed both with a variety of missiles and kinetic or beam weapons. They are often accompanied by destroyer or they are part of a bigger formations.
Battleships
The biggest starhips togheter with carriers, with the most firepower, the battleships are enormous starship that usually comes with a dedicated squadron attached. They are usually used only for major actions as they employment is costly. A single battleship on planetary orbit can wreak havoc against an enemy colony.
Carriers
Carriers are the corresponding of the sea carriers used in the XX century on the oceans of Earth. They are huge starships that hosts Fighters and/or Bomber groups and they usually comes with a squadron of destoyers attached.
