USS M-31

The USS M-31 was a Federation starship built to secifications of a "Galaxy" class vessel, meaning it was designed to traverse extragalactic voids, in this vessel's particular case, a mission to the M-31 Galaxy in 2285. (TOS novel: Star Trek II: The Wrath of Khan (novelization))
 * Presumably, this "Galaxy" class's name was not referring to a class of vessels created after a prototype named USS Galaxy (since that would contradict, or at least confuse, the nomenclature of the later 24th century Galaxy class starship); it could be presupposed the name referred to the purpose of the series of ships, since the names of the entire class were mentioned (with Galaxy'' not among them), and all three had an exploratory mission planned in another galaxy.


 * Sister ship USS Magellanic Clouds was mentioned, and, as "Magellan''" in TOS novel: Star Trek III: The Search for Spock (novelization), had reached its destination later in 2285. This is contradictory with speeds and principles much later in TNG that made extragalactic travel an improbability in the 24th century.