As of 2018, who has been the only U.S. naval officer to hold the rank of "Admiral of the Navy"?

George Dewey was born in 1837, graduated from the U.S. Naval Academy in 1858. He served during the American Civil War, participating in the Capture of New Orleans and the Siege of Port Hudson, rising to the rank of Lieutenant Commander by the end of the war.

In 1896, following different postings, he was promoted to Commodore and assigned command of the U.S. Asiatic Squadron. Dewey's preparation prior to the Spanish-American War allowed for the Asiatic Squadron strike at the Spanish fleet in Manila Bay at the beginning of the war in 1898. The attack by the American squadron ended with the Spanish fleet being completely defeated, with only the loss of one American sailor.

Honors and promotions were given to Dewey following the battle, he was promoted to rear admiral in May 1898, and to full admiral in 1899. In 1903, by Act of Congress, Dewey was promoted to the special rank of Admiral of the Navy and had the rank applied retroactively back to 1899. The rank was considered the equivalent to John Pershing's General of the Armies. He served on the General Board of the U.S. Navy from 1900 until his death in 1917.