The Harbinger, a Resurgent-class Star Destroyer, functioned as a vessel within the First Order Navy. This Star Destroyer possessed engines for propulsion. Before its destruction in 34 ABY, the Supremacy, a Mega-class Star Dreadnought and the mobile base of operations and flagship for the First Order, was at one time escorted by the Harbinger, among other ships.
The reference book Star Wars: The Last Jedi: Incredible Cross-Sections, authored by Jason Fry and with illustrations by Kemp Remillard, initially introduced the Harbinger in 2017.