The first references to an English navy occur in 851, when chroniclers described Wessex ships defeating a Viking fleet. These early fleets were limited in size but grew in size in the 10th century, allowing the power of Wessex to be projected across the Irish Sea and the English Channel; Cnut's fleet had as many as 40 vessels, while Edward the Confessor could muster 80 ships. Some ships were manned by sailors called lithesmen and bustsecarls, probably drawn from the coastal towns, while other vessels were mobilised as part of a national levy and manned by their regular crews. Naval forces played an important role during the rest of the Middle Ages, enabling the transportation of troops and supplies, raids into hostile territory and attacks on enemy fleets. English naval power became particularly important after the loss of Normandy in 1204, which turned the English Channel from a friendly transit route into a contested and critical border region. English fleets in the 13th and 14th centuries typically comprised specialist vessels, such as galleys and large transport ships, and pressed merchant vessels conscripted into action; the latter increasingly included cogs, a new form of sailing ship. Battles might be fought when one fleet found another at anchor, such as the English victory at Sluys in 1340, or in more open waters, as off the coast of Winchelsea in 1350; raiding campaigns, such as the French attacks on the south of England between 1338 and 1339, could cause devastation from which some towns never fully recovered.