The Starfleet 31st Fleet was a military unit, a fleet group of the Federation Starfleet during the Dominion War. The starships of the 31st were instrumental in keeping Cardassian and Jem'Hadar warships away from Vulcan while Admiral Salok's 5th Fleet forces did battle in the oort cloud of the Vulcanis system, in the First and Third Battles of Vulcanis. (Last Unicorn RPG module: The Dominion War Sourcebook: The Fires of Armageddon)