Prior to the Rebel Alliance's strike on the Second Death Star, the Dorneans were approached by Alliance leadership asking for aid. The Dorneans had a strong naval tradition dating back to their pre starflight days that includes both exploration and more martial endeavors.
The Dornean Navy was embroiled in their own war with the Empire, but decided to lend two ships to the cause; the Braha'tok and her sister ship, the Torktorak.
The two ships fought in the thick of the fighting during the Battle of Endor. Once the Liberty was destroyed by the second Death Star's super laser, the two ships moved into a defensive position to protect rescue efforts. They fought off three Raider Corvettes attempting to capture prisoners from the survivors of the Liberty, taking heavy damage in the process of destroying the three Imperial ships.
After the battle, the Braha'tok was unfit to travel back to the Dornean homeworld. Rather than scuttle the ship, the nascent New Republic offered to repair the ship in exchange for the services of it and its crew with the Vigilant Task Force. Captain Kiles L'toth took a vote of his 75 crewmen, and they unanimously chose to show the rest of the galaxy what a ship of determined Dorneans could do.