Fisher, John Arbuthnot (1841-1920), was a British admiral. He joined the Royal Navy in 1854 and served during the Crimean War (1853-1856). He became first sea lord, the United Kingdom's highest naval officer, in 1904. His reforms included a change from coal-burning to oil-burning warships and the introduction, in 1906, of the Dreadnought class of battleship. See Battleship.