Alfred Thayer Mahan (/məˈhæn/; September 27, 1840 – December 1, 1914) was a United States naval officer and historian, whom John Keegan called "the most important American strategist of the nineteenth century.

Mahan's works encouraged the development of large capital ships — eventually leading to dreadnought battleships — as he was an advocate of the 'decisive battle' and of naval blockades.

Before entering on his duties, College President Rear Admiral Stephen B. Luce pointed Mahan in the direction of writing his future studies on the influence of sea power.

Though he was prepared to become a professor in 1886, Luce was given command of the North Atlantic Squadron, and Mahan became President of the Naval War College by default (June 22, 1886 – January 12, 1889, July 22, 1892 – May 10, 1893).

Mahan sought to resurrect Horatio Nelson as a national hero in Britain and used his biography as a platform for expressing his views on naval strategy and tactics.

[22] In the 19th century, the United States sought greater control over its seaborne commerce in order to protect its economic interests which relied heavily on exports bound mainly for Europe.

Mahan's framework derived from Jomini, and emphasized strategic locations (such as choke points, canals, and coaling stations), as well as quantifiable levels of fighting power in a fleet.

Mahan also believed that in peacetime, states should increase production and shipping capacities and acquire overseas possessions, though he stressed that the number of coal fueling stations and strategic bases should be limited to avoid draining too many resources from the mother country.

Such a strategy called for the concentration of naval forces composed of capital ships, not too large but numerous, well-manned with crews thoroughly trained, and operating under the principle that the best defense is an aggressive offense.

His theories, expounded before the submarine became a serious factor in warfare, delayed the introduction of convoys as a defense against the Imperial German Navy's U-boat campaign during World War I.

Mahan's analysis of the Spanish-American War suggested to him that the great distances in the Pacific required the American battle fleet to be designed with long-range striking power.

This concentration of the U.S. fleet would force the British to tie down such a large proportion of their navy to watch the New York exits that other American ports would be relatively safe.

Although his history was relatively thin, based as it was on secondary sources, his vigorous style, and clear theory won widespread acceptance of navalists and supporters of the New Imperialism in Africa and Asia.

Given the rapid technological changes underway in propulsion (from coal to oil and from reciprocating engines to turbines), ordnance (with better fire directors, and new high explosives), and armor and the emergence of new craft such as destroyers and submarines, Mahan's emphasis on the capital ship and the command of the sea came at an opportune moment.

[29] Before 1914, Tirpitz completely rejected commerce raiding as a strategy and instead embraced Mahan's ideal of a decisive battle of annihilation between two fleets as the way to win command of the seas.

[8] However, the naval warfare of World War I proved completely different than German planners, influenced by Mahan, had anticipated because the Royal Navy avoided open battle and focused on blockading Germany.

As a result, after the Battles of Heligoland Bight and Dogger Bank, Admiral Hugo von Pohl kept most of Germany's surface fleet at its North Sea bases.

The Navy's part in securing victory was not fully understood by French public opinion in 1918, but a synthesis of old and new ideas arose from the lessons of the war, especially by Admiral Raoul Castex (1878–1968), who synthesized in his five-volume Théories Stratégiques the classical and materialist schools of naval theory.

He reversed Mahan's theory that command of the sea precedes maritime communications and foresaw the enlarged roles of aircraft and submarines in naval warfare.

Mahan believed that if the United States were to build an Isthmian canal, it would become a Pacific power, and therefore it should take possession of Hawaii to protect the West Coast.

[41] Between 1889 and 1892, Mahan was engaged in special service for the Bureau of Navigation, and in 1893 he was appointed to command the powerful new protected cruiser Chicago on a visit to Europe, where he was feted.

[42] As a delegate to the 1899 Hague Convention, Mahan argued against prohibiting the use of asphyxiating gases in warfare on the ground that such weapons would inflict such terrible casualties that belligerents would be forced to end wars more quickly, thus providing a net advantage for world peace.

As President, Mahan prevented the construction of a Confederate shipping canal in Nicaragua and opined that the main problem with republics is that "over time, the voters are apt to get tired of paying for what their country needs to defend itself".