Supremacy

The Supremacy, disparagingly nicknamed "Snoke's Boudoir," was a Mega-class Star Dreadnought that served as the flagship of Supreme Leader Snoke and the mobile headquarters of the First Order.

Dimensions
The Supremacy was 60 kilometers in wingspan and was the sole Mega-class Star Dreadnought in the First Order's service. Being the First Order's headquarters, the starship acted as both a command center and a battleship. Its size was gargantuan, easily outclassing all known ship sizes in galactic history, including the Star Dreadnoughts of the Galactic Empire, the trophy battlecruisers used by wealthy citizens of the waning days of the Old Republic, and even the various reconstructed versions of the flagship used by Xim the Despot.

Complement and crew requirements
The Supremacy was large enough to dock eight Resurgent-class Star Destroyers, six externally and two internally. It also crewed over 2,225,000 personnel, including officers, stormtroopers, gunners, vehicle engineers, factory workers, technical specialists, and communications staff.

Largely because of its role as the First Order's headquarters, not only was it able to carry stormtroopers into battle, but it was also capable of fixing, harboring, and building various ships in the First Order Navy onboard its hangar bays, two of which were large enough to even house and repair Resurgent-class Star Destroyers inside them. Aside from these, it also carried production lines, shipyards, army training grounds and even R&D labs.

Bridge
Its main command bridge sat upon a massive structure sitting at the center of the ship, which had a similar design to that of the Mandator IV-class Siege Dreadnought, and to a lesser extent the Resurgent-class Star Destroyer. The bridge had access to displays that allowed for 360 degree views, thus allowing for lookouts over everything within the city-scape-like structures on the main "wing" of the destroyer.

Hyperspace tracker and armaments
The Supremacy was able to track its targets through hyperspace using a combination of technological advances and brute-force data crunching. The Shipboard Tracking Control Complex boasted the data-shifting power of a planetary intel hub, linking its huge computer arrays to data banks loaded with centuries of combat reports and astrogation data. A static hyperspace field generated around the machines then accelerated their processing power to unheard-of levels. A target's last known trajectory yielded trillions of potential destinations, but the system could assess them with terrifying speed. This capability of tracking ships via hyperspace routes had its roots from the Tarkin Initiative. The ship, owing to it being the central command ship, forwarding base, and the proverbial brain of the First Order's entire forces, also was entirely self-sufficient, to the extent that it did not need to worry about supply shortages. In addition, the vessel possessed thousands of heavy turbolasers, anti-ship missile batteries, heavy ion cannons, and tractor beam projectors.

Construction
The ship was built by the First Order to act as the official capital of the First Order at the order of Snoke. Although various enlisted officers as well as allies of the First Order argued for a planet to act as their capital, Snoke insisted on using the Supremacy as the main capital of the group, at least until they succeeded in their goal of bringing the entire galaxy under their control and restoring the old Galactic Empire.

Cold war
Upon being completed, the Supremacy was kept hidden in the galaxy's Unknown Regions to keep it from being discovered. Snoke preferred to issue commands from this vessel to his minions. In order to ensure it wasn't discovered, Snoke also had it hidden among the brightest stars within the Unknown Regions. However, the Resistance nonetheless suspected the existence of the ship, nicknamed "Snoke's Boudoir" and tried to investigate the veracity of its rumored existence, although even the more cynical members of the Resistance could not imagine just how gargantuan the ship was. Prior to his defection to the Resistance, FN-2187 spent some time aboard the Supremacy whenever his stationed vessel, the Resurgent-class Star Destroyer Finalizer, was docked in the vessel, doing patrol routes and basic duties. After the Hosnian Cataclysm, however, Snoke, determining that the time was right to unveil himself, proceeded to unveil the ship to the unsuspecting galaxy to pursue the Resistance.

Attack on the Resistance fleet
The Supremacy participated in pursuit of the fleeing Resistance fleet. Under the command of General Armitage Hux, Supremacy followed the fleet, knowing they could not jump to hyperspace, as Supremacy could trace them with new technology and that if the Resistance continued to run, they would eventually run out of fuel. Utilizing single heavy turbolaser batteries near the forward hangars, the Supremacy bombarded the Resistance as they ran, destroying a medical frigate and a corvette when they ran out of fuel.

Eventually, the Resistance evacuated their flagship, Raddus in transports. Hux then ordered the transports targeted instead of the flagship. While many transports were destroyed, in Hux's haste to stop the Resistance from fleeing to Crait he neglected to realize that Vice Admiral Amilyn Holdo was preparing a jump to hyperspace while aimed directly at the Supremacy. Realizing too late what was about to happen, Hux could only watch as the Raddus sliced through about half of the ship, destroying several escorting Resurgents in the process as well.

This happened because the Supremacy used shields similar to that of Starkiller Base. Thus, there was a refresh rate that allowed objects to get through the shields if they traveled faster than light. The Supremacy lost its entire right half, and a huge gap was open to space where thousands of crew members and stormtroopers perished. However, due to Snoke's foresight, a large portion of the First Order was able to escape.

Behind the scenes
The ship was first unveiled via the BB-9E App-Enabled Droid toy by Sphero by going through various areas and collecting data. The initial data erroneously claimed that the length of the Supremacy was over 60km, although the confusion was rectified by Pablo Hidalgo on his Twitter feed where he clarified that the measurement was actually referring to the ship's width via its wingspan.

Appearances

 * Star Wars: Episode VIII The Last Jedi
 * The Last Jedi: Rose and Finn's Secret Mission

Non-canon appearances

 * Star Wars: Droid Repair Bay