The Excalibur, then under the command of Captain Prax, was one of the ships assigned to defend Earth from the Varkolak fleet in 2256. During the crisis, Cadet Hikaru Sulu was assigned to the vessel as relief helm officer. Sulu convinced Prax to listen to Spock's Priority One order to stand down from engaging the Varkolak fleet, despite the Excalibur being targeted by twelve different Varkolak vessels. (ST - SA novel: The Assassination Game) The Excalibur was part of the Starfleet force that battled starships of the Romulan Star Empire in the 2250s. (TOS video game: D-A-C)