John Davis Long, American lawyer and politician, 34th United States Secretary of the Navy (d. 1915)
John Davis Long (October 27, 1838 – August 28, 1915) was an American lawyer, politician, and writer from Massachusetts. He was the 32nd Governor of Massachusetts, serving from 1880 to 1883. He later served as the Secretary of the Navy from 1897 to 1902, a period that included the primarily naval Spanish–American War.

Born in Buckfield, Maine, Long was educated as a lawyer at Harvard University, later settling in Hingham, Massachusetts. He became active in Republican Party politics in the 1870s, winning election for the state legislature in 1874. He rose rapidly in prominence, and was elected lieutenant governor in 1879 and governor in 1880. He advocated modest reforms during his three years as governor, which were relatively uneventful.

After returning to private practice he was offered a cabinet post by his friend, President William McKinley, in 1896. He chose to become Secretary of the Navy despite lacking detailed knowledge of naval matters. He clashed with his Under-Secretary, Theodore Roosevelt, over expansion of the Navy when the Spanish–American War broke out in 1898. He resigned the post after Roosevelt became president, and resumed his law practice. He died at his home in 1915; his publications include a lifelong journal, a history of the Spanish–American War, and a verse translation of Virgil's Aeneid.