The shipyard assault was an attack by the Confederacy of Independent Systems on Fondor, more specifically, Fondor Shipyards, where a Star Destroyer of an unknown class was being constructed, known as the Xerxes, in 22 BBY. The Confederate Navy amounted an attack as soon as possible, after Separatist Intelligence found out about the Galactic Republic's plan to built a large warship with cloaking devise to use as a flagship. In reality, Supreme Chancellor Palpatine was using it as an excuse to test several technologies for the future Executor-class Super Star Destroyer.
A team of Mandalorians from Death Watch that were in temporary service of the Separatists, used the vulture droid attack as cover to get aboard the Xerxes. They proceeded to move through the vessel, killing many clone troopers along the way, and destroyed the main reactor. They escaped, and the massive vessel exploded minutes later. The commander of the ship, Captain Yarus, who was on the shipyards at the time, was later executed by Palpatine on Coruscant for "incompetence". The Chancellor, as Darth Sidious, gave Count Dooku a scolding for allowing the attack to occur.