Xerxes

The Xerxes was a Star Destroyer of an unknown class very similar to the Executor-class Super Star Destroyer. It was developed in 22 BBY by Fondor Shipyards, and was under construction secretly over Fondor, by orders of Supreme Chancellor Palpatine himself. Officially, the reason for it's creation was to create a new, advanced command vessel to counter the battleships used by the Confederacy of Independent Systems. But in actuality, the vessel was ordered to be created by Palpatine for the sole purpose of acting as a prototype Super Star Destroyer. He hoped to also test three large cloaking devices aboard the Xerxes, and placed it under command of Captain Yarus, an experienced officer.

However, the Separatists discovered the vessel and amounted a raid on the vessel during which they placed a team of Mandalorians from Death Watch aboard. Making their way through the vessel, and killing numerous clone troopers and officers along the way, they were able to destroy the vessel by sabotaging the main reactor; escaping aboard a stolen shuttle. Palpatine was angry with Count Dooku for allowing it to happen, and had the commander, Captain Yarus, secretly executed.