The Nebula-class Star Destroyer, also known as the Defender-class Star Destroyer, was the largest, most powerful warship design in the New Republic’s New Class Modernization Program.
Development of the Nebula-class Star Destroyer began shortly after the fall of Coruscant. Formally renamed as the Defender when it was made a part of the Defender design program, the Nebula-class refined the core elements of Walex Blissex’s Republic-class design into a smaller, more angular hull. The Defender program was derailed by delays caused by political distractions and the campaigns of Grand Admiral Thrawn and the reborn Darth Sidious. When work eventually resumed the design became part of the New Class program and lent its hull design to the Endurance-class carrier. In 15 ABY, the Nebula-class became the last of the eight new starship designs of the New Class to enter service. The ship’s introduction was said to be ill-timed, as it occurred during what was considered to be the most peaceful year since the founding of the New Republic.
The first of the class to enter service was the Obi-Wan, named after one of the Rebellion’s heroes, Obi-Wan Kenobi. The ship was commanded by Captain Whyrrryk, a female Wookiee. Due to the process of building compact yet powerful warships of this sort, only a small number of Nebula-class ships were built. Only ten were in service c. 17 ABY, with projections of one more being launched each year until the New Class build program was completed. When the Yuuzhan Vong invaded, the few ships of the New Republic’s valuable Nebula-class were kept close to the Core Worlds in reserve fleets due to political pressure. Despite this, Nebulas performed well in clashes with the extra-galactic warships once they finally did see combat. Even considering its age, the Nebula-class still represented the peak of modern, efficient Star Destroyer design during the Yuuzhan Vong War.
At least one Defender-class Star Destroyer was still in service by the time of Darth Krayt’s Galactic Empire. Pol Temm maintained the ship as part of his The Wheel defense fleet. Attempting to enforce his no-weapons rule, he entered a space battle with a Mandalorian faction called the Mandalorian Supremacists and was reportedly killed when his Defender blew up.