Classis Britannica The Classis Britannica ( literally , " British fleet " , in the sense of ' the fleet in British waters ' or ' the fleet of the province of Britannia ' , rather than ' the fleet of the state of Britain ' ) was a provincial naval fleet of the navy of ancient Rome . Its purpose was to control the English Channel and the waters around the Roman province of Britannia . Unlike modern ( and some contemporary Roman ) " fighting navies " , its job was largely the logistical movement of personnel and support , and keeping open communication routes across the Channel . There is no literary reference in the classical historians to the " Classis Britannica " by that name , and archaeological evidence is also tantalizingly scant ( although tiles stamped CLBR are common along the east Kent coast and in London , suggesting either government buildings or an early instance of army surplus ) , meaning that details of its history and form are unfortunately based on a large degree of interpretation . History . Invasion . A fleet was originally raised for the invasion of Britain under Claudius , with the task of bringing an invasion force of 40 , 000 men from the Roman army , plus supplies , to Britain . It continued after the successful invasion to provide support for the army , shuttling massive quantities of supplies across the English Channel . Conquest . This fleet played a major role in the subsequent conquest of Britannia . However , Tacitus states that strangely , about twenty years after the invasion , it was not present at Suetonius Paulinus ' s crossing of the Menai Strait to Anglesey before the Boudican Rebellion . This suggests the force was still occupied in the Channel area , unsuitable to the long voyage up to north Wales , or too small by then to offer any useful level of support to the ground troops . In the Flavian period what had been raised initially as a temporary invasion fleet was formalised as the " Classis Britannica " and made permanent in statute . Also in the Flavian period , under the governor Agricola , it circumnavigated Scotland , and in 83 attacked the eastern coast of Scotland . One year later the fleet is recorded as having reached the Orkney Islands . Due to the lack of serious naval opposition in the early Imperial period in the area of the fleet ' s operations - the invasion crossing , for example , went navally uncontested - the Classis ' s main role was as logistical support both to the army in Britannia , and also to armies campaigning in later years in Germania . Hiatus . The fleet disappears from the archaeological record towards the middle of the 3rd century but is known from contemporary sources to have continued in existence after this date . Carausius . In 286 , Carausius , a Roman military commander of Gaulish origins , was appointed to command the " Classis Britannica " , and given the responsibility of eliminating Frankish and Saxon pirates who had been raiding the coasts of Armorica and Belgic Gaul . However , he was suspected of keeping captured treasure for himself , and even of allowing the pirates to carry out raids and enrich themselves before taking action against them , and Maximian ordered his execution . In late 286 or early 287 he learned of this sentence and responded by usurping power and declaring himself emperor of Britannia and northern Gaul . When the British fleet was attacked by a German and French fleet representing the Roman Empire , the British fleet was victorious , showing that it must have been substantial at the time . The would - be invaders , however , blamed poor weather for their defeat . By 300 , however , Britannia was once again a part of the larger Roman Empire , and the " Classis Britannica " restored as a Roman imperial fleet . End of empire . In the final years of Roman Britain , the fleet was devoted almost entirely to protecting the Eastern and Southern coasts of Great Britain against first piratic actions and , shortly before the withdrawal of troops from Britain , against Saxon raids against coastal towns and villages on what came to be known as the Saxon Shore . The fleet probably had some role in the operation of the Saxon Shore Forts . Ports and harbours . It was originally believed that the main base of the fleet was in Richborough but more recent archaeological work has uncovered one of only three surviving forts occupied by the fleet ' s marines at Dover , suggesting this was in fact a major base of the Classis . It may even have been its primary base , though one of the other surviving fleet forts , at Boulogne - sur - Mer , is far larger and thus said by some to be a more likely contender than Dover for that role . Portus Adurni ( which was later adapted and known as Portchester Castle ) at the north of Portsmouth harbour is another contender and believed to have been at the very least a major base for the fleet .