Super Star Destroyer (Executor) 

      Made by Kuat Drive Yards, the Super Star Destroyer was the largest traditional starship made by the Imperial Navy.  At 8000  meters (this figure is disputed, nobody is sure of the actual length), it was only outsized by the Death Stars and torpedo spheres.  These huge ships were Imperial Navy command ships which were assigned to only the most important and prestigious missions.  Being assigned to one of these ships, especially the Executor, was considered a fast track to promotion.
      The Super Star Destroyer is somewhat impractical in a military sense, as smaller ships could accomplish the job.  They were more of a symbol of the Emperor's unlimited power and resources.  While the Imperial Star Destroyer frightened worlds into submission, the Super Star Destroyer terrorized them beyond the capability of resistance.  The SSD was so intimidating that it could win a battle without engaging the enemy and conquer without firing a shot. 
      SSD's were very heavily armed.  It had over a thousand weapons including turbolasers, concussion missile tubes, tractor-beam projectors, and ion cannons.  They carried two wings, or 144 Tie craft, and 200 other support and combat craft.  It was just as prepared for ground assaults with a full corps of Stormtroopers, 38,000 ground troopers, 3 prefabricated garrison bases, and enough walkers to decimate any enemy base.

      Another famous SSD is the Lusankya, the Imperial prison ship commanded by Ysanne Isard.  The ship was buried under Coruscant's surface until it was escaped from by Rouge Squadron pilot Corran Horn.  After his escape, Isard raised the ship out of its sanctuary into orbit, causing huge amounts of damage to the surface and orbital defenses in that section of orbit.  After harrasing the New Republic for a time, it was nearly destroyed in the Battle of Thyferra.  It was surrendered to the New Republic, repaired and re-commissioned. 

      Warlord Zinji had a SSD he used as a flagship, the Iron Fist.  He also attempted to steal another SSD which was under construction from Kuat Drive Yards, called the Razor's Kiss.  This ship was destroyed as Zinji attempted to escape.  He later used its wreckage, wired together into a rough-looking star destroyer to cover the Iron Fist's escape from a battle and go into hiding.