A recently published history of naval power and trade in the Mediterranean in the early medieval period provides a reminder of that vital but little-explored change in the balance of maritime power which preceded the Crusades and of the movement which won back for the Christians of the West, Sardinia, Sicily, and Malta, threatened the shores of Africa and Albania, and was both a rehearsal and an essential preliminary for the great Drang nach Osten which was to follow. Little is known of the shipping used in these operations or of the tactics employed, but an attempt has been made to investigate the scanty sources for the Norman naval operations in the early stages of their conquest of southern Italy and Sicily, not merely because some of these operations were important in their immediate results, but also as an example of the naval technique of the Latin Christian military commanders in southern Europe. The subject derives additional interest from the spectacle it affords of Vikings finding their sea-legs again after many decades as farmers and cavalrymen in Normandy. It also offers one explanation for the conquest of the considerable area of southern Italy and Sicily by a comparatively small force, and once again demonstrates the eclecticism and adaptability of the Normans.