In becoming "a useful man" on the maritime stage, Matthew Fontaine Maury focused on the ills of a clique-ridden Navy, charted sea lanes and bested Great Britain's admiralty in securing the fastest, safest routes to India and Australia. He helped bind the Old and New worlds with the laying of the transatlantic cable, forcefully advocated Southern rights in a troubled union, and preached Manifest Destiny from the Arctic to Cape Horn. And he revolutionized...