This volume provides a comprehensive guide to three major theatres of combat; the battles for the Atlantic, the war in the Mediterranean and the contest in the Indian Ocean. The war at sea was a vital contest, which if lost would have irreversibly altered the balance of the military forces on land. An island nation like Britain could not have sustained itself to triumph over Germany, Italy and Japan after five years of fighting without having first assured victory at sea. The sea lanes were the logistical arteries of British and subsequent Allied armies fighting on the three continents of Africa, Asia and Europe. The Second World War was ultimately won by land forces but it could always have been lost at sea.