Dreadnaught-class heavy cruiser

The Dreadnaught was an older class of capital ship that served under the Old Republic, measuring six hundred meters in length. Despite being out of date, they remained in service in the Imperial Navy as a second line craft and by the Rebel Alliance through the Galactic Civil War. It was over-crewed for its size, and perhaps the most hilariously misnamed ship in the history of the Star Wars universe.

Katana Fleet

A modestly sized prestige fleet created by the Old Republic, the Katana Fleet was composed solely of modernized and heavily automated dreadnaughts. The renown of this so-called "dark fleet" remains unexplained, but may relate to hopes of the Katana Fleet's technology eventually seeing widespread use, reducing the crew requirements of older Republic vessels.

This heavy automation came with a price, however: driven to insanity by a virus, crewmembers on the flagship ordered the entire fleet to simultaneously jump to hyperspace, a disaster made possible through the pervasive use of slave circuits.

The Katana Fleet resurfaced in 9 ABY, where its elements were largely claimed by forces under Grand Admiral Thrawn.

Modernization

Despite the Katana Fleet disaster, a lack of capital ships forced the Rebellion to adopt their own conversion programme. This resulted in the so-called Rebel Assault Frigate, an overall more capable vessel.