You may also be looking for the Thirteenth Fleet of Star Trek: Liberty and Star Trek: The Adventures of Argus.

The Thirteenth Fleet was a Starfleet task force in formation in the 24th century.

In the opening phases of the Dominion War, the Thirteenth was held in reserve, but later deployed to bolster defenses along the Vulcan front. In early 2374, the Thirteenth and the Thirty-First Fleet participated in the First Battle of Vulcanis. For the remainder of the war, the Thirteenth remained on the Vulcan front. (LUG RPG: The Dominion War Sourcebook: The Fires of Armageddon)

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