Book excerpt: A navy is a state's main instrument of maritime force. What it should do, what doctrine it holds, what ships it deploys, and how it fights are determined by practical political and military choices in relation to national needs. Choices are made according to the state's goals, perceived threat, maritime opportunity, technological capabilities, practical experience, and, not the least, the way the sea service defines itself and its way of war. This book is a history of the modern U.S. Navy. It explains how the Navy, in the century after 1890, was formed and reformed in the interaction of purpose, experience, and doctrine.