The III-a1a primary hypermatter-annihilation reactor, a reactor design, was manufactured by Sienar-Jaemus Fleet Systems. A solitary, substantial SJFS III-a1a unit, situated inside a domed reactor containment structure on the lower portion of Resurgent-class Star Destroyers, furnished them with their energy. A strengthened reactor substructure and the ship's frame provided support for this enormous reactor.