USS Mjolnir
From Star Trek: Theurgy Wiki
The USS Mjolnir was a 24th century Federation starship operated by Starfleet. In 2375, the Mjolnir was posted near the old Delphic Expanse and used as a science vessel. Natalie Stark rode out the tail end of the Dominion War aboard her, working her way through the Engineering and Operations departments as natural wartime attrition opened up new career opportunities for her.
(It has not been revealed what class the Mjolnir was but it given the fact that it was kept off the war front it seems that it was an older class of vessel such as a Centaur, Constellation, Miranda, or Oberth class.)