Tector-class Star Destroyer

The Tector-class Star Destroyer was class of Star Destroyer in the service of the Galactic Empire's navy. The Harbinger was a ship of this class.

History
In 4 ABY, the Tector-class Harbinger was part of the Imperial Navy's fleet defending the second Death Star over the moon of Endor. After the Rebel Alliance launched an assault on the seemingly incomplete station, which was actually a trap engineered by Emperor Palpatine designed to destroy the entirety of the rebellion at once, the Harbinger was destroyed by advancing rebel ships. Shortly after, the space station itself was destroyed, along with a large portion of the gathered Imperial forces.

Behind the scenes
In Star Wars Legends, the Tector-class was first referenced in Star Wars: Revenge of the Sith Incredible Cross-Sections, a 2005 reference book. The first new canon source to use the name Tector-class was "The Levers of Power," a 2015 short story written by Jason Fry and included in the compilation book The Rise of the Empire. On Twitter, Fry confirmed his authorial intent that a hangarless Star Destroyer seen in Star Wars: Episode VI Return of the Jedi is supposed to be the Tector-class Star Destroyer Harbinger.