Alfred Thayer Mahan (September 27, 1840 – December 1, 1914) was a United States Navy admiral, geostrategist, and historian, who has been called "the most important American strategist of the nineteenth century
Commissioned as a lieutenant in 1861, Mahan served the Union in the American Civil War as an officer on USS Worcester, Congress, Pocahontas, and James Adger, and as an instructor at the Naval Academy. In 1865, he was promoted to lieutenant commander, and then to commander (1872), and captain (1885).