In 2375, the location of Starbase 375 was labeled on a tactical cartography map that was displayed in the wardroom of Deep Space 9. Starbase 375 was located approximately thirty light years from Cardassia Prime, twenty-five light years from Bajor, and fifty-five light years from Ferenginar. (DS9: "When It Rains...", okudagram)
Following the Second Battle of Deep Space 9 and the subsequent withdrawal of Federation and Klingon forces from Deep Space 9 in late 2373, the USS Defiant, under the command of Captain Benjamin Sisko, was recalled to this starbase for reassignment. Captain Sisko was stationed here as adjutant to Admiral William Ross after Ross relieved him of command of the Defiant. This starbase was also the location of a Jem'Hadar attack ship retrieved by Sisko a year prior from Torga IV. (DS9: "A Time to Stand")
Approximately four months later, Starbase 375 served as gathering point for the Second and Fifth Fleets in preparation for Operation Return, in which combined Federation and Klingon forces managed to retake Deep Space 9. Sisko then returned to his previous post as commander of Deep Space 9. (DS9: "Favor the Bold", "Sacrifice of Angels")
Background information Edit
The Star Trek: Deep Space Nine Technical Manual includes a directory for Starbase 375 that was created, but seen only in the background of Admiral Ross' office, for "Behind the Lines". It lists several Deep Space Nine production staff members as Starbase 375 personnel, including Camille Argus, Bob Blackman, Jerry Bono, Mary Ellen Bosche, Valerie Canamar, Ed Cooper, Phyllis Corcoran, Russ English, Derek Garth, Steve Gausche, Bill Gocke, Phil Jacobson, Brian Johnson, Ralph Johnson, Ronnie Knox, Carol Kunz, Don Lehman, Mark Overton, Todd Overton, Cleo Severy, Jim Unsinn, Michael Westmore, Jack White, Murphy Wiltz and Edmond Wright.
A visual of the Jem'Hadar attack ship docked inside the base also shows two Starfleet personnel present in the docking area. This may suggest that the docking area can be cut off from space, perhaps through use of a force field.
According to the Star Trek: Star Charts (p. 47) and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"; "The Dominion War: Strategy and Battles, 2373-75"), Starbase 375 was located in the Alpha Quadrant. During the Dominion War, this starbase was the Fifth Fleet headquarters.