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Multiple realities
(covers information from several alternate timelines)

A list of unnamed Federation starships of the Galaxy-class.

Utopia Planitia, Mars

Partially constructed starship

In 2370, in an alternate quantum reality, these unassembled starship components, consisting of a saucer section, secondary hull, and warp nacelles, were on the surface Utopia Planitia facilities on Mars. (TNG: "Parallels")

The painting for the surface was created by Rick Sternbach and Mike Okuda. (Star Trek Encyclopedia (2nd ed., p. 21))
The intention of the artwork was to depict a Galaxy-class ship under construction. When asked if construction indeed was intended to take place on the surface of Mars, Okuda acknowledged:

"Yes, that was the intent, although I like the suggestion that it might have been a training facility. It was something that Rick and I put together in Photoshop. I don't recall exactly who did what, but I remember that the upper image uses a bunch of simple paper models that we made for use as [...] generic futuristic city buildings for exactly this sort of image. Rick may remember more about this. I do recall that we wondered how the components would be brought into orbit, whether they'd be beamed up, hauled up by space elevator, or carried by a huge orbital tug […]

"It [surface construction] certainly would be difficult, and I personally think that it would be more likely that the major component assembly would be done in orbit. I believe that Rick felt this way, too. Still, impulse engines routinely accelerate starship masses (many tens, even hundreds of thousands of tons) to large fractions of the speed of light in very brief times. This suggests a propulsion technology many thousands of times more powerful than anything we have in the 21st century. Also, structural integrity fields would need to protect against these accelerations, which conservatively would exceed 1,000 gees. As a result, I'd contend that lifting major starship components into orbit from the surface of Mars would be well within the reach of Star Trek's postulated technology." [1](X)

In Sternbach's explanation of the painting, he suggested it to be a "systems integration simulator," adding, "the hardware seen on the surface could be the real vessel parts, which were probably only 20% filled with "stuff" and then lifted into orbit for final assembly. If not, then they are flight-quality hardware used as a functioning lab to make sure everything works as designed." [2]

Utopia Planitia Fleet Yards

A Galaxy-class (right, center) under construction at Utopia Planitia Fleet Yards

In 2371, at least two starships were docked at the Utopia Planitia Fleet Yards in orbit of Mars. (VOY: "Relativity")

One of the ships was seen enclosed in a drydock similar to Earth Station McKinley from TNG: "Family" while yet another was seen in a drydock not unlike that from Star Trek: The Motion Picture. Additionally, the uncompleted saucer section seen right as the episode opens may be that of a Galaxy-class ship, as suggested in the 2002 Ships of the Line calendar.

Second Fleet

Several Galaxy-class ships in the Second Fleet

In late 2373, several starships belonged to the Second Fleet.

While the Dominion attacked Deep Space 9 during the second Battle of Deep Space 9, several of these vessels crossed the Cardassian border and destroyed the Dominion shipyards on Torros III. These ships later joined with the USS Defiant and IKS Rotarran following the evacuation of DS9 for a counterattack against the Dominion forces. (DS9: "Call to Arms")

Starbase 375

Galaxy-class starships preparing to participate in Operation Return

Ten, possibly more, of these starships were in the vicinity of Starbase 375 in 2374 and in the fleet that participated in Operation Return. (DS9: "Favor the Bold", "Sacrifice of Angels")

Stationed at DS9

These two starships were stationed at Deep Space 9, along a Vor'cha-class attack cruiser, several Miranda-class starships, and a Bajoran interceptor, in mid 2374. One of these ships later left the general area after the ship's positions had changed. (DS9: "You Are Cordially Invited")

Later these starships, along with two Miranda-class starships and the Bajoran interceptor, were again present at DS9. (DS9: "The Reckoning")

Prior to the first Battle of Chin'toka, these two starships were joined by three D'deridex-class Warbirds, three Klingon Birds-of-Prey, three Miranda-class starships, and a Bajoran interceptor. (DS9: "Tears of the Prophets")

In early 2375, one of the two departed that station, while the other remained, along with a Vor'cha-class attack cruiser, and four Romulan warbirds. (DS9: "Image in the Sand")

First Battle of Chin'toka

Several Galaxy-class departing for Chin'toka

These starships, including the USS Galaxy and USS Venture, were involved in the first Battle of Chin'toka in late 2374. (DS9: "Tears of the Prophets")

Battle of Cardassia

A Galaxy-class ship firing phasers

In 2375, this starship participated in the Battle of Cardassia. It fired its phasers at the enemy Dominion ships. (DS9: "What You Leave Behind")

Escorts for USS Voyager

A Galaxy-class (upper left) escorts Voyager

In mid-2378, this starship was stationed near the Sol system were dispatched by Admiral Owen Paris to a defensive point near an opening Borg transwarp aperture near Earth.

This and the other ships present opened fire on the emerging Borg sphere and assisted in its destruction. Following the emergence of USS Voyager from the debris, this vessel assisted in escorting Voyager back to Earth. (VOY: "Endgame")