The Defiant-class starship was a heavily-armed, limited-role Starfleet vessel, developed in response to the Borg threat as originally encountered in 2365, and spurred on by the shocking results of the Battle of Wolf 359 in 2367. The USS Defiant was the class prototype. It was Starfleet's first dedicated combat vessel, and therefore did not house provision for families or diplomatic missions, nor science labs or recreational facilities.
The Defiant-class was a heavily-armored, stripped-down starship and incorporated the latest in Starfleet weaponry and defensive technology and was equipped with a class-7 warp drive. The Defiant was considerably smaller than most other Federation starships.
The warp core spanned three decks in the aft section of the ship.
The bridge layout of the Defiant was compact, but nonetheless accommodated the familiar engineering, tactical, science, conn, and ops stations. The entire module was sunken into a much larger Deck 1 than on most Federation starships to provide added protection during combat situations. Access to the bridge was provided by two doorways at the back, located on both port and starboard sides. The port side of the bridge housed the engineering and tactical I stations, while the starboard side featured the science and tactical II consoles.
The center of the bridge featured the lone captain's chair, which was on a raised platform and had a clear view of all bridge stations, as well as of the main viewscreen. On both sides of the command chair were separate control panels, allowing the occupant access to virtually every system aboard the ship.
Between the command chair and the viewscreen was an integrated flight control and operations panel, capable of performing the joint duties of those stations' larger counterparts on other Federation starships.
The main sickbay was located on Deck 2 between the mess hall and science labs. Containing four biobeds, this room served as the primary crew support facility during emergency situations. The room was equipped with limited surgical facilities and was primarily intended to stabilize patients until they could be delivered to a nearby friendly starbase medical facility.
Crew quarters: Each cabin was equipped with one replicator port and one standard computer terminal. Crewmembers had to share their quarters with at least one other crewmate during normal times of operation.
Ships of the Defiant-class lacked any sort of recreational facilities, and the only place for informal gathering were the two mess hall areas located on the port side of Deck 2.
Defiant-class ships were equipped with two transporter rooms, one located on deck 1 and the other on deck 2
A total of four phaser cannon assemblies were located in forward-facing locations on board Defiant-class vessels. The cannons were located above and below the nacelle root attachments on the main body on both port and starboard sides of the ship.
The standard phaser beam emitters aboard Defiant-class vessels served almost as a secondary supplement to the primary phaser cannon array. In all, the Defiant-class was equipped with at least three emitters: one forward and aft, as well as one behind the bridge on the dorsal surface.
The Defiant-class vessels' deflector arrays could also be refitted into a makeshift phaser emitter, providing one-shot capability in extreme emergency. The phaser emission was generated by the nose/deflector unit.
Defiant-class vessels had a total of six torpedo launchers, four forward and two aft.
The Defiant-class was equipped with deflector shields.
At least one Defiant-class vessel, USS Defiant NX-74205, was equipped with ablative armor.
A special amendment to the Treaty of Algeron allowed the USS Defiant to be fitted with a Romulan cloaking device.
Defiant class starships
USS Wessex is a Defiant-class starship. Below is some information about that class: why it was designed and built; the bridge layout and its personnel; and the Defiant class defences, which included ablative armor and a cloaking device. Here is a link to the Star Trek wiki at Memory Alpha.