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A carrier is a general ship classification, with warships of different sub-classifications within the UNSC and Covenant fleets. Such a vessel is formally defined as "a large warship carrying fighters equipped with flight decks for takeoffs and landings". There are multiple classes of carrier within this general designation. The term "carrier" is not limited to starships, as there are still seaborne carriers in service with humanity.
Typically the size of cruisers or larger, the general combat role of a carrier in combat is analogous to that of a seaborne aircraft carrier; to deploy starfighters, such as Seraphs or Longswords. Aside their fighter complements, carriers also possess weapons themselves, to protect themselves in combat when their fighters are unable to defend them. In planetary occupation missions, carriers are mobile deployers of ground forces to subjugate an enemy planet, launching dropships and top-cover fighters.
The navies of the UNSC and the Covenant have different classifications of carriers. For example, Covenant CAS-class assault carriers are on the scale of five kilometers long while CSO-class supercarriers can have a length of around 29 kilometers, giving a scale of the keel length of carrier-type warships. In the Covenant, carriers typically serve as the flagship of a fleet, while in the UNSC, the role is more commonly—though not invariably—filled by cruisers. However, supercarriers still form the core of major expeditionary fleets, with carriers filling a similar role for smaller battle groups and defensive fleets. In the Covenant fleet, the heavy-tonnage carrier classes DDS, CAS, and CSO are all classified as part of a "supercarrier" category distinct from lighter carrier vessels that fulfill support roles.
The Covenant are known to possess unidentified light carrier classes.