Registry: ISS Enterprise / NCC 1701
First Seen On: Star Trek and Star Trek: Enterprise (TV series: 2001-2005)
Forget the United Federation of Planets, this battle-cruiser is the flagship of the Terran Empire, an imperialistic version of future humanity inhabiting an evil mirror universe. The ship is almost identical to the USS Enterprise, except its registry replaces USS with ISS (said to indicate United Star Ship and Imperial Star Ship, respectively).
We learn that this Enterprise has pain booths to punish wayward crew members, and sports dagger emblems on its sliding doors. The mirror-universe concept — a staple of Trek writers — is revisited in Star Trek: Enterprise when Captain Archer and crew later (but actually earlier, because Star Trek: Enterprise comes chronologically before Kirk’s era) comes into contact with an evil version of the NX-01 Enterprise.