The New Republic would capture a good number of Imperial Star Destroyers after the Battle of Endor, many of which would go on to serve in the ranks of the New Republic's navy, where their strength, size, and abundance of these vessels made them useful assets. However, most would undergo substantial modifications to mitigate design flaws and keep them relevant over their service lives.

Modelled above is the ISD Challenger, a refitted Imperial I-class commissioned originally as the Conqueror and captured by the Rebel Alliance relatively intact at a dockyard during the push into the core worlds. Substantial time, energy and resources went into refitting the Challenger as a main-line heavy warship, inspired by the Tector-Class Star Destroyer line.

The propulsion system and power grid was radically overhauled, with much of the hangar space being replaced with a battlecruiser-tier reactor. This allowed for the installation of triple-layered Mon Calamari shield generators and the relocation of the octuple barbettes to a 'turbolaser ridge' rising to the superstructure. Ventral Ion cannons and prow torpedo launchers add to the impressive armament and added some much-needed versatility to a relatively inflexible design.

(Part 2 in my series of New Republic Midi-scale ISDs. Renders available at https://imgur.com/a/80xsLfK .)