- For other uses, see Excalibur.
In the year 2268, the Excalibur was ordered to test the new M-5 multitronic computer that had been developed. One of the tests was to participate in wargames against several other starships, including the ISS Enterprise. During the wargames, the M-5 computer supposedly malfunctioned and launched an assault with full weapons power against the Enterprise. The Enterprise was able to survive the assault, and Captain Spock later suspected it was an attempt to assassinate him. (TOS - Mirror Universe novel: The Sorrows of Empire).
The Excalibur remained under the malfunctioning computer's control for decades afterwards, in the Daystrom Testing Grounds, where the vessel was stored. Excalibur was one of the four starships in M-5's fleet that assaulted the ISS Excelsior in the 2290s decade. (TOS video game: Shattered Universe)
- ISS Excalibur seems to be the mirror universe counterpart of the USS Excalibur (NCC-1664), a Constitution-class starship, in service in the 23rd century.