This volume occupies a special place in maritime history since it represents a first attempt on a popular level to present an overall survey of the rich, diverse, and exciting development of European naval and maritime power during the Middle Ages. Though a number of general surveys exist which deal with the navies and shipping of antiquity, except for the excellent though highly technical recent book by Richard Unger, The Ship in the Medieval Economy 600-1600, such surveys are lacking for the thousand years which represent medieval times.
Very much focused on warfare, not trade. Some stories about merchant convoys, but nothing about tonnages or rates, increases in capacities and the like. Very non-technical and non-quantitative. Which makes it a nice read, even though, compared to the knowledge of the authors in 1985, we now already some more details from recent research.