English engineer who was a major figure in developing techniques for manufacturing radar components.

In 1900 Fleming went to the United States to undergo training at the Westinghouse Electric and Manufacturing Company, East Pittsburgh, Pa. Upon returning to England in 1902 he joined the British Westinghouse Company, later called the Metropolitan-Vickers Company, Manchester, where he worked as an insulation expert and later as a transformer designer.

During World War I Fleming made important advances in submarine-detection gear, and for this work he was appointed Commander of the Order of the British Empire in 1920. A pioneer in the development of radio, in 1920 he established in Manchester the second British transmitting station to broadcast programs on a daily basis. From 1931 to 1954 he served as director of research and education at Metropolitan-Vickers. He established Metropolitan-Vickers' research department and made sweeping innovations in engineering education. His work on demountable, high-power thermionic (thermionic power converter) tubes made it possible to establish radar stations in Great Britain by the time World War II began in 1939. He was knighted in 1945.