This chapter on seaborne transport in the Second World War pursues four thematic lines of development. First, in accordance with the scope of the conflict, it places the history of transport on a global and often globally interlocked scale. Second, to capture the distinctive challenges of the Second World War, the chapter compares the two world war experiences. Third, while the story of the maritime Allied nations dominates, it comprehends Axis cross-sea traffic. Finally, the chapter places the experience of the war within a broader temporal perspective which looks back to pre-war maritime infrastructures of knowledge, expertise, networks and installations and forward to the post-war maritime consequences of five years of global war at sea. Two matters cloud any discussion of global transport in the Second World War. One is the ultimate victory of the Allies. The other is the cornucopia of statistics trumpeted in nearly all the histories of that triumph.