Trekipedia

I.S.S. Defiant NCC-1764 (Mirror)

In the Mirror Universe, the Terran Imperial Starship Defiant was in service in the 23rd century. The Defiant was destroyed by a Tholian force led by Loskene in 2268, after Loskene had demanded the Defiant retreat. Its recorder beacon was recovered from the Defiant‘s wreckage by the I.S.S. Enterprise NCC-1701. Despite standard precedure to retaliate against any military that attacked a Terran vessel, the Empire did not respond to this particular attack, per the recommendation of Captain Spock to Emperor John Gill, in light of the Empire’s greater concern at the time with the growing Klingon-Cardassian Alliance.^[1] It’s unclear if this Defiant is the prime reality starship, having remained in service for over a century after arriving back in time, or a newer Constitution-class vessel with the same name.