The ISS Enterprise (NCC-1701) was a Constitution Class ship in the 2260s in the mirror universe. It was was virtually identical to the Enterprise (TOS) except for the Terran Empire Markings on the doors and walls as well as the armed guards in the corridors. In 2266, a landing party from the main universe beamed up during an ion storm an ended up on the ISS Enterprise. They later got back and the mirror universe landing party was returned.