The crew of the USS Conquest come upon the Sojourn some time after the Battle of the Celestial Temple (as it came to be called) when her captain decided to check up on the long-lost research facility of Herschel 36. Not long after entering the nebula in which the station is located, Conquest captain Alitrine Jenner comes across one of Herschel's projects - the Sojourn - apparently inoperable and adrift. Upon beaming aboard, they activate the central computer, and to much surprise, find that the ship is a sentient being.
The computer recalls its experience with some difficulty, as it was unable to save the inhabitants of Herschel. Soon after the Dominion took control of the Federation briefly in the Dominion war of 2376, a Jem'hadar battle cruiser happened upon the station much by accident, it would seem. The crew immediately sounded the alert and prepared to evacuate via the only warp-capable vessel available, the USS Etruria. Sojourn wanted to help, and attempted to hold off the attackers to give the Etruria time to escape.
It didn't work out too well. Sojourn inflicted respectable damage on the enemy vessel before a well-placed shot overloaded her power grid and tripped a failsafe, isolating the computer in order to protect it from overload. The last thing the Sojourn remembered was the Jem'hadar ship moving toward the Etruria as she tried to get her engines online.
A sensor sweep of the area confirmed Sojourn's fear - wreckage of the Etruria was present, not only floating in space, but several pieces had impacted themselves into the unarmored portions of Sojourn's hull. Considering that everything was undisturbed since that day, it seemed logical to conclude that the Dominon ship was destroyed as well, therefore keeping Herschel secure.
At this point, Sojourn seems like a valuable asset to the Federation, and she is hastily assigned to wartime duty. It is a possibility that more of these vessels will be produced in the future; this has not yet been confirmed, however.
