ISS Enterprise
In the fictional Star Trek universe, the I.S.S. Enterprise is a starship from the Mirror Universe reality.
I.S.S. is short for "Imperial Star Ship".
In the Original Series
In The Original Series, the ship in almost every way, appeared as an exact duplicate of the Federation starship U.S.S. Enterprise, except for the ominous logo of the Terran Empire that was seen on doors and bulkheads throughout the ship. Some interior scenes were darker and filled with devices of punishment and torture, such as agony booths and the mirror-Captain Kirk's deadly Tantalus device.
Since the Empire was more about conquering space than peacefully exploring it, Imperial ships differed with more powerful weapon systems than the Federation would consider putting on their vessels.
The ship was seen in the Star Trek: The Original Series episode Mirror, Mirror.
In Enterprise
In Star Trek: Enterprise, the Mirror Universe ship in almost every way appeared as an exact duplicate of the Enterprise (NX-01). Differences included the use of a cloaking device captured from the Suliban, escape pods, a tractor beam as opposed to a grappler, and a torture booth created by the mirror Doctor Phlox and Malcolm Reed. It was commanded by Captain Maximilian Forrest, although for a brief time his first officer, Commander Jonathan Archer, took command following a mutiny. This Enterprise is destroyed by the Tholians. See In a Mirror, Darkly.