Dreadnaughts are large, ancient heavy cruisers that originally were commissioned by the Old Republic. These six-hundred-meter-long ships were among the largest ships in the Old Republic Navy before the introduction of the Victory Star Destroyer. While the cruisers are slow and poorly armed by modern starship standards, a number of Dreadnaughts had been refitted over the years for service in both the Empire and the Rebel Alliance.
The standard Dreadnaught in the Imperial Navy was not significantly different from the original ship the Old Republic had used. The ship maintained ten turbolaser cannons, twenty quad turbolaser cannons, and ten turbolaser batteries. Even after refitting, a Dreadnaughts sublight speed barely matched that of the Victory Star Destroyer. The hyperdrive had a slow Class Two rating, and the hull and shields were weak for a ship of its size. Refitted Dreadnaughts still required a crew of 16,000 soldiers. The Empire was able to construct flight decks in most of its Dreadnaughts, allowing them to carry a squadron of twelve TIE fighters. Imperial Dreadnaughts were normally assigned to patrol duties in outlying portions of the Empire or sent to protect supply convoys.
With the advent of Grand Admiral Thrawns quest to capture the Katana fleet of Rendili StarDrive Dreadnaughts, historians around the galaxy showed renewed interest in this "cursed" battle fleet, known as "the Dark Force" because of its dark gray hull surfacing. Each Katana Dreadnaught was completely refitted with slave-rigging units. This reduced each ships crew to about 2,000 soldiers, but it also tied each ships vital systems into a central computer. One Dreadnaught could seize control of the entire fleet and that is exactly what happened.
A hive virus quickly spread through the fleet, driving the victims insane; the Katana fleet crew members slaved their ships together and jumped into hyperspace, disappearing for nearly half a century. Only after the New Republic contacted Talon Karrde was the Dark Force rediscovered, but Grand Admiral Thrawn had already learned the location of the Katana fleet. The empire captured most of the two hundred ships, and Thrawn filled the Dreadnaughts with his clone stormtroopers, giving the Imperial Grand Admiral a decisive advantage in his own campaign against the New Republic.