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   The Defiant-class began as part of Starfleet's response to the threat from the Borg; encountered by USS Enterprise-D in 2365. The Advanced Starship Design Bureau began development of the class at the Antares Fleet Yards in 2366. During development the Defiant-class was classified as an escort class of starship. In reality, ships of this class were small, heavily armed, and exceptionally powerful warships with an extremely limited, yet simple role: Borg supression.

   In order for ships of the Defiant-class to perform adequately; the six custom-built hulls would have a multilayer ablative armor surrounding them and would be armed with pulse phaser cannons, photon torpedoes and the newly developed quantum torpedoes. The six custom-built Defiant-class ships would also be equipped with upgraded defensive shields & sensor technology. The ships would also be equipped with a launchable photon torpedo warhead module that could be used in an extreme situation. Bearing registry number NX-74205, the class prototype was commissioned in late 2368 (early 2369) as USS Defiant. However, design flaws discovered during the prototype's shakedown cruise and a decrease in the threat from the Borg led Starfleet to abandon the project and “moth-ball” the Defiant.

   In 2371 the threat of a possible invasion of the Alpha Quadrant from the Dominion of the Gamma Quadrant loomed. To counter this threat, Starfleet activated the Defiant; placing it under the command of Commander (later Captain) Benjamin Sisko and assigning the vessel to space station Deep Space Nine as part of a first line defense for the Alpha Quadrant. As part of this “first line defense” of the quadrant, USS Defiant was equipped with a cloaking device on loan from the Romulan Star Empire under the condition that all intelligence gathered by Starfleet about the Dominion be distributed to the Empire. This gave Defiant the distinction of being the sole Federation starship in Starfleet service equipped with a cloak at the time.

   Following the early successes of the Defiant-class prototype, Starfleet built at least four of the six custom-built ships by the end of 2375. The Defiant itself would have an exemplary service record which included participation in: the Federation-Klingon War of 2372-73, the Borg invasion of Sector 001 (Earth) in 2373 and the costly Dominion War of 2373-75. Unfortunately, the Defiant-class prototype would be destroyed in combat by the Dominion's Alpha Quadrant allies, the Breen, in late 2375. Just prior to the ending of the war with the Dominion, another Defiant-class vessel, USS Sao Paulo, took the prototype's place at DS9 and fought in the final battles of the war as USS Defiant, NX-74205, under special dispensation from Starfleet Operations.

   When the Dominion War began in late 2373, the Defiant-class vessel, USS Valiant (NCC-74210), was “behind enemy lines” during a training mission being conducted by members of an elite group Starfleet Academy cadets, known as “Red Squad” under the supervision of a small number of Starfleet officers. Within the first year of the war in 2374, the Valiant was attacked and damaged by a Dominion-Cardassian ship and the small number of officers were killed. Just prior to dying, the commanding officer ordered the senior cadet to return to Federation space, however, the cadet chose to continue the assigned mission of tracking down a rumored Dominion Jem'Hadar battleship to gather data about the potentially deadly vessel. While tracking the battleship, the Valiant rescued two individuals travelling aboard a Starfleet Danube-class runabout, an officer and civilian from space station DS9. A few days after the rescue, the Valiant detected, intercepted, and gathered the data on the Jem'Hadar battleship. Instead of returning to the fleet with the data, the senior cadet in command chose to attack the ship using the data his crew had gathered. The attack failed and the Valiant was destroyed with nearly all hands. The only survivors were the DS9 personnel and one cadet.

   In 2379, Starfleet created “Battle Group Omega” to confront a possible Reman invasion of the Federation from the confines of the Romulan Star Empire. Of the seven vessels that constituted the battle group, a Defiant-class ship bearing registry number NCC-75418 and commissioned as USS Valiant was a part of the group. Ultimately, the battle group was not needed due to the successful actions of the Enterprise-E and its crew.

Ships of the Class

NOTES

   USS Valiant (75418) — This vessel is mentioned, but not seen, in the franchise's tenth film, Star Trek: Nemesis. In the film, the ship is part of “Starfleet Battle Group Omega” and its registry number is displayed on the viewscreen of the Enterprise-E's astrometrics lab. The Star Trek Encyclopedia (2016) suggests that it is an Intrepid-class ship however, Memory Beta indicates the vessel is Defiant-class. Due to the ship's registry number being in proximity to the Sao Paulo's, the InfoBarn assumes that this vessel is of the Defiant-class, just like its' immediate predecessor.