STARSHIP
ISS Excalibur
Class:	Constitution-class
Registry:	NCC-1664
Affiliation:	Imperial Starfleet
Status:	Unknown

In the mirror universe, the ISS Excalibur (NCC-1664) was an Imperial Starfleet vessel in service in the 23rd century.

In 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 later Captain Spock suspected it was an attempt to assassinate him. (TOS novel: Glass Empires: 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. (TOS 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.

Early series of Constitution-class class I/class XI heavy cruiser starships
Federation Starfleet (primary universe)	Built to mk I specifications	Constellation • Constitution • Defiant • Endeavor • Enterprise • Excalibur • Exeter • Farragut • Hood • Intrepid • Kongo • Lexington • Potemkin • Republic • Valiant (I) • Yorktown
	Various specifications	Alexander • Asimov • Brahe • Confederate • Enterprise (Vardaine copy) • Glory • Indomitable • Isshasshte • Jefferson • John F. Kennedy • Nautilus • Olympus Mons • Ortisei • Pathfinder • Surak • Tao Feng • Trojan • Venture • Zimbabwe • unnamed Constitution-class starships
Terran Empire Starfleet (mirror universe)		Carnage • Banshee • Defiant • Enterprise • Excalibur • Hood • Kodos • Lexington • Nobunaga • Potemkin
See also the later subclasses: Bonhomme Richard-subclass (mk II) • Achernar-subclass (mk III) • Tikopai-subclass (mk IV) • Enterprise-subclasses (mk I-III refits) • other Constitution variants