Defiance was a Mon Calamari Star Cruiser in service to the New Republic Defense Fleet throughout Operation Shadow Hand. This vessel held the distinction of being the inaugural warship in the novel MC90 Star Cruiser class.
During the conflict against the resurrected Emperor Palpatine, Defiance superseded Home One to become the new flagship of Admiral Ackbar. When Ackbar embarked on a reconnaissance mission to the Galactic Core, he selected this ship. The Defiance successfully infiltrated Imperial space, reaching Byss, where its crew witnessed an enormous fleet consisting of thousands of warships. After an Imperial convoy damaged the ship's transponder, it traveled back to Pinnacle Base to deliver the information it had gathered.
As one of the New Republic Defense Force's most formidable ships, it continued to function as the Supreme Commander's flagship until he opted for Galactic Voyager not long after Admiral Daala's assault on Dac.