D'deridex Class
The D'deridex-class warbird was the pinnacle of Romulan engineering and power in the mid-24th century. First introduced into the Romulan fleet in the 2350s, the D'deridex was a largely guarded secret, decades in the making, and required many other predecessor classes as testbeds for technologies eventually deployed, together, on the famous warbird.
Following the Romulan supernova, the D'deridex is largely only seen utilized by the remnants of the Romulan Star Empire faction within Romulan space.
Exploration and Science
Although designed primarily as an intimidating warship, the D'deridex is fully capable of carrying out any mission asked of it. The D'deridex fields an impressive sensor array which allows it to be an overly capable exploratory platform. The sensor array's primary purpose was intelligence gathering across the Neutral Zone, however, as the years went on warbird commanders found the D'deridex's sensors to be versatile and capable enough to handle nearly anything that their missions required.
While the D'deridex wasn't built with missions of science in mind, the ship is more than capable of handling almost any mission of exploration thrown at it.
Diplomacy
Much like its scientific endeavors, the D'deridex wasn't built with diplomacy in mind unless you count the Romulan adage of "peace through superior firepower". However, at times, the D'deridex has had to be utilized for diplomatic functions as the flagship class. Over the years, the Empire was able to refine the D'deridex and transform sections of it in order to better adapt to the growing need for diplomatic functioning. While nowhere near the capabilities of the Galaxy-class, the D'deridex performs adequately enough in the face of being a warship.
Engineering
For decades, the D'deridex served as the primary flagship class of the Romulan Star Empire, carrying out missions of scientific endeavor, diplomacy, and combat. The original purpose of the D’deridex also explains its size — it was entirely meant to use its size to intimidate foes on the battlefield. The D’deridex was designed to be larger than anything the Federation or Klingon Empire fielded at the time or reasonably would in the coming decades.
In addition, the D'deridex was the first ship in the Romulan fleet to field the modern artificial quantum singularity power plant. While previous classes had also used it, none had been able to power a vessel nearly as large or impressive as the D'deridex.
Tactical
As a warship, the D'deridex primarily utilizes its versatile forward disruptors in combat. Additionally, it fields additional disruptors in every quadrant of the ship giving it 360 degrees of coverage. Each disruptor is capable of firing in both beam and burst mode with the main forward nose disruptor equaling energies of the main phaser array on a Galaxy-class starship. The warbird's disruptors are complemented by standard plasma torpedoes, a robust shielding system, and a Romulan cloaking device. The cloaking devices on the D'deridex's were state of the art at the time of the class's construction, and over the years have gone through many upgrades paving the way for future generations of cloaking devices. However, the ship's size and power plant made for a recipe that requires all D'deridex's that are traveling at warp to stay under warp 5 in order to avoid detection while at warp.
Shipboard Life
For a ship built primarily for combat, the D'deridex is surprisingly comfortable for its 1,500+ crew.