The Eternal Flagship was a capital ship that served as the flagship of the Eternal Fleet under the command of Arcann, Prince and later Emperor of the Eternal Empire. Commissioned by Arcann's father, Emperor Valkorion at the height of his rule, the Eternal Flagship is the vanguard of the Eternal Fleet and a powerful symbol of Zakuul might and splendor. While the rest of the fleet is piloted by GEMINI droid captains, the Eternal Flagship is operated by the most skilled and zealous humans in the empire.
Famously, the Eternal Flagship transported Arcann and Thexan to battle during their conquest of the Core Worlds. The flagship swiftly knocked out Balmorra's planetary defense system, allowing the twin princes to capture the world's weapon factories intact. In recognition of this momentous victory, the flagship's crew was awarded Zakuul's highest honor, the Medal of Eternal Valor, by none other than the Immortal Emperor Valkorion.
In 3632 BBY, Arcann took his flagship and a significant detachment of the Eternal Fleet to intercept the Outlander, who was attempting to take a lone Eternal Fleet warship. By the time they arrived and opened fire, the Gravestone had escaped into hyperspace. Subsequently, Arcann's flagship lost control of all Eternal Fleet vessels outside their sector, as the remainder had fallen under the control of SCORPIO.
SCORPIO gave Arcann information on the location of Odessen, the home base of the Alliance. As Arcann's fleet approached Odessen, the Alliance Commander, along with his closest comrades, approached it in the Gravestone. After clearing a path, the Outlander, along with Lana Beniko and Senya Tirall boarded the flagship. The Outlander got separated from his team when SCORPIO revealed she had total control of the fleet, firing at the flagship. The Outlander then fought his way to Arcann and defeated him with both the power of Valkorion and Satele Shan and Darth Marr, but before he could end the battle, part of the roof crushed Arcann. As the Outlander made his way to a fighter in the hangar, Senya Tirall got her son out from the debris, when she was confronted and nearly killed by Vaylin. While Vaylin threw herself toward her mother, Arcann woke up and pushed her back, similar to the way their brother had stopped Arcann from killing Valkorion 5 years earlier.
Senya made her way to a shuttle in the hangar with the injured Arcann. The Outlander faced a decision about whether or not to let them live, with Koth Vortena pleading with them to fire on the shuttle before it jumped to hyperspace. The remnants of Arcann's Fleet formed up for a combined attack of an unknown type, as the Gravestone fired, interrupting and obliterating them. The resulting explosion nearly destroyed the Outlander, their crew and the Gravestone.