The Thalassa, serving under Admiral Sander Delvardus, was a battlecruiser of the Praetor Mark II-class.
Due to the Empire's preference for Star Destroyers and dreadnoughts, the Thalassa was among the limited number of _Praetor Mark II_s constructed. Its construction and commissioning occurred sometime following the conclusion of the Clone Wars.
Many years afterward, following the Battle of Endor, Delvardus utilized the Thalassa during his campaign as a warlord. During the seizure of Moorja, the battlecruiser engaged a New Republic fleet. This fleet included EF76 Nebulon-B escort frigates and Y-wing bombers. This combined force successfully destroyed the Thalassa above Moorja. This loss was just one in a series of setbacks for Delvardus, which soon led to him being driven from the territory he had seized along the Rimma Trade Route.