A Mirror Universe ship, the I.S.S. Enterprise operated under the command of Captain Forrest and was the flagship of the Terran Empire in the mid-22nd century. Its mission was to defend the Empire from a rising rebellion against Terran rule, from such factions as certain Vulcan and Andorian cells.
The vessel was armed with a Suliban cloaking device, which enabled the NX-01 to fire weapons while cloaked. I.S.S. Enterprise also featured an impressive array of weaponry, including several phaser and photon banks.
Along with main engineering and a more militaristic bridge module than its "normal universe" counterpart, the ship featured the "Agony Booth," a disciplinary interrogation tool that could stimulate the pain center of any humanoid, causing the subject to experience severe and varying levels of pain. A synaptic scan callibrates the Booth for each species, thus making each subject's "experience" unique.
First Officer Jonathan Archer managed to usurp command from Captain Forrest, and commandeered the vessel in order to investigate reports that the Tholians had in their possession a starship from both the future and an alternate reality.
Upon discovering the future starship (the Defiant) at a secret Tholian spacedock facility, Enterprise was caught in a Tholian web and destroyed, with Captain Forrest at the conn.