The Thirty-First reinforced the Fifth Fleet in the Vulcanis system during the First Battle of Vulcanis. These reinforcements plus those from the Thirteenth Fleet gave the Federation the forces necessary to counter attack against the Dominion's position. The Thirty-First remained at Vulcan until at least the Third Battle of Vulcanis. (LUG RPG: The Dominion War Sourcebook: The Fires of Armageddon)