Katana was a Dreadnaught-class heavy cruiser

Dreadnaught-class Heavy Cruiser Starship Starship Models

that served in the Judicial

Galactic Republic Judiciary Organization Grand Army of the Republic

Starfleet of the Old Republic. It was the flagship of the fleet

Katana Fleet Organization Grand Army of the Republic

that bore its name.
Long before the Clone Wars, it was lost with the rest of the fleet due to the outbreak of a hive virus that caused the crew of the Katana to go mad and jump to random hyperspace coordinates, along with the other 199 slaved ships. That fleet was called the Katana Fleet or, in the Rebellion era, the Dark Force.
Although the fleet was rediscovered around 9 ABY, and the majority captured by the Empire, the Katana herself was one of the 15 ships recovered by the New Republic. During the Battle for the Katana fleet

Battle for the Katana fleet Event New Republic Era

, a team led by Luke Skywalker

Luke Skywalker (Human) Character Major Characters

was able to use the Katana to destroy the Imperial I-class Star Destroyer

Imperial-class Star Destroyer Starship Starship Models

Peremptory, by Han Solo

Han Solo (Human) Character Major Characters

using its slave circuit controls to ram one of the other Dreadnaughts into the Star Destroyer.