A Battleship is one of the largest vessels any fleet can muster. These gargantuan ships can be twenty megameters in length and carry millions of crewmen; they typically mount the largest and most powerful weapons of any ship. This class encompasses several classes of Imperial and Chaos battleships, the largest Eldar, Necron, Tau, and Tyranid vessels, and the largest mass class of Ork ships. Battleships typically fall under one of two headings: carriers or gunships.

A carrier battleship, the classic example being the Imperial Emperor-class, has some weapons but those are mostly defensive; its main weapon is its massive set of launch bays that can pour forth thousands of fighters, bombers, and assault shuttles. A gunship battleship mounts large arrays of heavy weapons and torpedo bays; this class includes Necron tombships, Imperial Apocalypse and Retribution-class vessels, Tyranid hiveships, and many others.

These ships are superseded by the even larger pre-Age of Strife advanced superships that are reserved for larger combat or exterminatus missions. Such ships are similar to the huge space forts, planetary sized battle-hulks, and doomsday bastions yet are far more mobile and capable of fighting like standard battlefleets. They are mustered in far greater numbers and utilize battleship sized escorts as part of far more powerful Devastation Blockades and Sentinal Forces, which routinely crush Hive fleets or Chaos daemonworlds, or guard dangerous powers on quarantined worlds. The most powerful ships are kept totally in secret shipyard-crypts such as the Caelan Class Sunderer vessel (rumored to be able to fire and anhilatate any target in any time or location, far too powerful to used except by the Emperor Himself) and other powerful doomsday-class voidships.