The U.S. became interested in a trans-isthmus canal in either Nicaragua or Panama and realized the need for naval protection. Captain Alfred Thayer Mahan was an exceptionally influential theorist; his ideas were much admired by future 26th President Theodore Roosevelt, as the U.S. rapidly built a powerful naval fleet of steel warships in the 1880s and 1890s. Roosevelt served as Assistant Secretary of the Navy in 1897–1898 and was an aggressive supporter of an American war with Spain over Cuban interests.