Image via WikipediaStarfleet's first true warship is the USS Defiant NX-74205 launched in 2366. What makes this tough little ship so special is it ablative armour capable of deflecting Borg firepower. The defiant class is incorporated with a state of the art multi targeting array, capable of reacting rapidly with modulating phaser frequencies designed to cut through even the toughest enemy shields. It was developed and built at the Mars Utopia Planitia Fleetyards under the watchful eyes of Commander Benjamin Sisco.
Sisco's Defiant was originally intended to fight the Borg thick skins with its multiple torpedo launchers. Earlier prototypes had a more conventional design, with the warp nacelles on out riggers. However this design is later abandoned in favor of a more compact disc shape which encases the nacelles. Work on the Defiant is halted after the Borg threat is averted in 2367.
In 2371 Starfleets finest engineers resume construction amid fears Dominion forces are invading Federation space. The prototype USS Defiant is far from ready to enter service, but because of the serious nature of the threat, she is assigned to Deep Space Nine where the engineering staff finalize Commander Sisco's design. Development of its quantum torpedo proves so effective in deepspace combat that it becomes standard issue and replaces all photon torpedoes in Starfleet vessels.
In direct violation of the treaty of Algeron, the Defiant is loaned a Romulan cloaking device which doesn't always work well with its ablative armour technology. In fact when in stealth mode or "Blue Alert" the crew has to avoid using the "high tech stuff" which generates emissions easily detected by enemy sensors.