In January 2374, Federation President Rosarev -- in his role as Commander-in-Chief of Federation forces -- ordered the Seventh, Ninth and Tenth Fleets to the Spinward Theater of Operations. (Dominion War Timeline: "Early Dominion Victories: January-June 2374")
The Tenth Fleet was tasked with the defense of Betazed and its outlying colonies during the Dominion War. In late-2374, the Tenth Fleet was caught off guard by an assault on Betazed by the Dominion that saw the world captured in ten hours. (DS9: "In the Pale Moonlight")
- According to at least one source, The Dominion War Sourcebook: The Fires of Armageddon, the Tenth Fleet was completely destroyed fighting to the last to give the Betazoids time to prepare for the invasion.
The Tenth Fleet was also the nickname for the Starfleet International chapters based in Region 10 — Alaska and Western Canada. (Starfleet International: Scott A. Akers, et al., Master Genealogy: Starfleet Region 10)