The Executor-class Super-class Star Destroyers, also referred to as the Executor-class Star Dreadnoughts due to their immense size, are assigned only to the most important missions. These ships are fully equipped and, essentially, serve as mobile fortress-cities. The Executor-class can terrorize worlds beyond the capability for resistance, able to conquer enemies without firing a shot as they see the folly of trying to battle against such a monster. They are one of the largest classes of ship ever built.
The Executor-class measures 19 kilometers in length and is 100 times more massive than an Imperial-class Star Destroyer. With over 5,000 weapon emplacements, and able to carry a staggering 864 starfighters, these 13-engine-ships have enough firepower to destroy entire fleets alone and are also used as command ships for Imperial Navy Fleets or planetary invasions. In a military sense, however, these vessels are somewhat impractical, since a smaller ship can fulfill its mission duties. Instead, the Executor-class symbolizes the Empire’s unlimited power and resources.
The Executor-class was the brainchild of Lira Wessex, the brilliant and ambitious engineer who already had the designs of the Venator-class and Imperial-class Star Destroyers to her credit. Following her work on the already-impressive Imperial-class, Wessex sought to improve on the design.
Adhering to Kuat Drive Yards' philosophy of psychological effect in starship design, or "terror styling", she believed that the immense size of an Imperial-class Star Destroyer was largely responsible for its ability to intimidate opponents. Working on that theory, she began designing a starship that would dwarf all her previous works. Though KDY had designed and built extremely large warships in the past, the result obtained by Wessex was utterly gargantuan.
Emperor Palpatine authorized the construction of the first four Executor-class ships even before the Battle of Yavin, but it still had to be slipped past the watchful eyes of various oversight committees in the Imperial Senate; to the very last, the minority of Senators who opposed Palpatine and his policies used the few political tools they had left to hinder him, and one of these was budget oversight.
To conceal the particulars of the vessel from the opposition, the Navy listed the new ship as a "Super-class Star Destroyer" in budget reports submitted to the Senate, and understated its true length (19,000 meters) by many kilometers. Thus the Executor-class and other ships of its size range became known by the nickname "Super Star Destroyers", and also why the ship's length, even in Imperial government scandocs, was variously reported, depending on the source, as 8,000 meters or 12,800 meters, before the true details of this behemoth came to light.
The sudden and unanticipated destruction of the Death Star at Yavin changed Wessex's production schedule completely. At the urging of Darth Vader, the Emperor ordered her to rush the new ships into production as quickly as possible, to compensate for the loss of the battle station. As certain segments of naval command may have anticipated, a new symbol of intimidation was needed, and as Wessex had believed, the Executor-class fit the need well.