From Star Trek: Theurgy Wiki
The USS Illithid was a Federation starship operated by Starfleet in the first decade of the 24th century. In 2309 the Illithid made contact with the Ash'reem when an anthropologic infiltration mission was discovered on their home world of Ash'kara. The situation resulted in a standoff in which several dozen rail guns designed for cargo transfer between the home world and the Kymira outpost were adjusted and aimed at the Illithid.
After several hours of negotiations an official apology broadcast to the Ash'reem people for the attempted deception of the scientists. Eventually he Ash'reem requested a more official and extended meeting of governments to discus the possibility of joining the Federation.
(It is unknown what class of starship the USS Illithid was but it is likely to be a late 23rd early 24th century vessel such as a Constellation, Excelsior, Miranda, or Oberth class. It is unlikely that the Illithid would still be serving in 2381.)