The starship was commanded by Captain Gabe Márquez in the early 24th century, and had a crew of 535 personnel. In the year 2319, Admiral John Harriman had the Cassiopeia diverted to Helaspont Station where the majority of the crew disembarked. Harriman then commandeered the ship for a personal mission to rescue Demora Sulu and the crew of the USS Excelsior from a planet on the other side of the Rejarran portal in orbit of Rejarris II. The Cassiopeia was destroyed when Harriman crashed it into the interdimensional portal in order to keep it, and the portal, from falling into the hands of the Tzenkethi Coalition. Ironically, it would be the very ship that Harriman commanded at one time, the USS Enterprise-B, had also become part of the plan and was the very vessel which rescued not only Harr