The Imperium of Man is divided into five fleet zones known as the Segmentae Majoris. Each Segmentum has a headquarters world called a Segmentum Fortress which forms the base of Imperial Navy operations within the Segmentum. The five major Segmentae Majoris are the: Segmentum Solar, Segmentum Ultima, Segmentum Tempestus, Segmentum Pacificus and Segmentum Obscurus.