USS Defiant is Destroyed
Star Trek: Deep Space Nine.
In Season 7, Episode 20. "The Changing Face of Evil"
A Starfleet, Klingon, Romulan force counter-attacks the Dominion (Jem'Hadar, Cardassian, Breen) assault in the Chin'toka system, Starfleet's last foothold in Dominion territory.