Gallons of ink have been used analyzing Adm. Alfred Thayer Mahan’s thoughts, his naval theories, and his contribution to sea power. One vital aspect of his life, however, has been ignored or misunderstood by many scholars: his religious faith. Mahan was a professing Christian who took his faith with the utmost seriousness, and as a result, his worldview was inherently Christian. He wrote and spoke extensively on religious issues, a point frequently ignored by many historians. This is a fundamental mistake, for a deeper and more accurate understanding of Mahan as a person and as a naval theorist can be gained by a meaningful examination of his religious beliefs. God and Sea Power is the first work to examine in a detailed and contextual way how Mahan’s faith influenced his views on war, politics, and foreign relations. All this material gives us a very full picture of his faith, a fascinating combination of born-again evangelicalism and High Church Anglicanism. Mahan was also an active layman in the Episcopal Church and these activities are discussed as well. Mahan’s father, Dennis Hart Mahan, was a West Point professor of engineering and military science for many years, and was a notable military figure in his own right. Mahan’s uncle, Milo Mahan, was a noted church historian and professor at General Theological Seminary. Both these men had a strong influence on Alfred and their lives and careers are discussed as well.