The U.S.S. Defiant was originally created to combat the Borg, but was used primarily in the defense of the space station Deep Space 9 from the Dominion. It is the only starship in Starfleet that has a cloaking device, which was donated by the Romulans. It is heavily armed for a ship of its size, and is able to out maneuver and outgun ships many times its size.
The Defiant helped defend Earth from the Borg cube during the Battle of Sector 001. The Defiant was severely damaged during the battle and Lieutenant Commander Worf ordered a suicide attack on the Cube before he and his crew were rescued by Captain Picard and the Enterprise. After the defeat of the Borg it was repaired and returned to Deep Space Nine.
The ship was destroyed by Breen and Jem'Hadar forces during the Battle of Chin'toka towards the end of the Dominion War.