It is a century since Mahan and his disciples taught the world that a battlefleet was indispensable to a great power. Great and not so great powers still keep powerful navies today, but we have no generally-accepted principles to explain why. In this book historians and naval officers from Britain, the United States and other countries study the use of naval power over a century, and ask what it is for, and what it can do. It will be essential reading for modern historians, policy-makers and strategists.