A small, heavily armed Starfleet escort first designed to fight the Borg, and a rare dedicated warship in the 24th-century fleet.
The Defiant-class is a compact Starfleet escort created after the Borg attack at Wolf 359. Benjamin Sisko helped design the prototype, the USS Defiant, as a warship meant to fight the Borg. It was over-powered for its size and the project was shelved, but the ship was assigned to Deep Space Nine in 2371 to defend against the Dominion. It carries pulse phasers, quantum torpedoes and ablative armour, and the Romulans lent it a cloaking device.
The original Defiant fought in many of the major clashes of the Dominion War and helped defeat the Borg cube that attacked Earth in 2373. It was destroyed by the Breen in 2375, and a sister ship, the São Paulo, was given the name Defiant and taken over by Sisko's crew. Other ships of the class, such as the Valiant, crewed by cadets, also fought in the war.
The Defiant-class marked Starfleet's open acceptance of dedicated warships. Its blunt, aggressive look matched the darker tone of Deep Space Nine, and ships of the class appear again in Picard.