Star Trek: 10 Most Powerful Ships
6. USS Defiant (Defiant Class)
The Defiant represented the first time that Starfleet developed a ship specifically for the purpose of combat.
After encountering the Jem'Hadar and their fighters for the first time, and losing a Galaxy class starship in the process, Sisko knew he needed more firepower. As such, he pulled a prototype ship out of mothballs called the Defiant. Technically categorized as an Escort vessel, the Defiant was designed solely for war, a role it took to quickly.
A smaller ship than most in Starfleet, the Defiant class was overpowered for its size. Since it was originally designed to fight the Borg, that actually makes a lot of sense. The ship had four phaser cannons, three phaser emitters, four forward facing torpedo launchers and two aft torpedo launchers. Defensively, the Defiant class ships had shields as well as ablative armor.
But the USS Defiant had one other trick up its sleeve that the rest of its class did not. As the first and only one of its line at the time, Sisko was able to cut a deal with the Romulans to use one of their cloaking devices. The condition was that the Federation would only use said cloaking device in the Gamma Quadrant, though once war broke out the Romulans were a lot more lenient on that rule.
After the first USS Defiant was destroyed in combat with the Breen, no other ships in that class ever had a cloaking device. But even without that capability, it remained one of the toughest ships in Starfleet.