Defiance replaced Home One as the flagship of Admiral Ackbar during the campaign against the reborn Emperor Palpatine. Ackbar took the ship when he ventured on a recon mission to the Galactic Core. The Defiance managed to penetrate Imperial territory as far as Byss, where it observed a fleet of thousands of warships. The ship's transponder was damaged by an Imperial convoy and the ship returned to the Pinnacle Base to report its finding.
One of the most powerful vessels in the New Republic Defense Force, the vessel remained the flagship for the Supreme Commander until he chose Galactic Voyager shortly after Admiral Daala's attack on Dac.