There is perhaps no greater symbol of the Empire's dominance, no greater argument for the futility of defiance than the colossal flagship of its mighty fleet, the Tarkin Doctrine epitomized, the Executor-class Super Star Destroyer. 

 Larger by a factor of ten than most imperial warships and wielding the firepower of an entire fleet, a single Executor-class was more than capable of engaging entire hostile battlegroups, and conducting full-scale planetary invasions without reinforcements. 

 Even without engaging in combat, the mere terrifying presence of the Executor-class has been known to inspire the immediate retreat or surrender to hostile forces, and as a means of maintaining order and security through fear, the ship was second only to the Death Star.

(My version of the introduction of the Executor)