John Battiscombe "J. B." Gunn (13 May 1928 – 2 December 2008), known as Ian or Iain, was a British physicist, who spent most of his career in the United States. He discovered the Gunn effect, which led to the invention of the Gunn diode, the first inexpensive source of microwave power that did not require vacuum tubes. He was born John Battiscombe Gunn, but only used that name in legal documents.