Carriers are dreadnought-sized vessels that carry a large amount of fighters. All races provide their fleets with organic fighter support. Cruisers fit a handful in the space between the interior pressure hulls and exterior armor. Dreadnoughts have a hangar deck within the hull.
In fleet combat, carriers stay clear of battle, launching fighters bearing disruptor torpedoes. Fighters are the primary striking power of the ship; if a carrier enters mass accelerator range of the enemy, things have gone very wrong.
It is possible to recover and rearm fighters during combat, though most carriers seal the flight deck and try to stay out of the way. The flight deck is essentially a corridor through the armor and into the heart of the vessel. A single well-placed torpedo is enough to gut a carrier.