Nimbosa was a large Imperial Civilised World roughly the size of the Sol System's gas giant of Saturn in the Ultima Segmentum of the galaxy that was overrun by the Tau in the late 41st Millennium and retaken by the Imperium during the successful Nimbosa Crusade that was led by elements from several Chapters of the Adeptus Astartes, including the Black Templars, Imperial Fists and the Ultramarines.