William Forbes-Sempill, 19th Lord Sempill

Who was William Forbes-Sempill, 19th Lord Sempill?

William Francis Forbes-Sempill, 19th Lord Sempill AFC, AFRAeS, was a British peer and record-breaking air pioneer who was later shown to have been a traitor who passed secret information to the Imperial Japanese military before the Second World War. Educated at Eton, he began his career as a pilot in the Royal Flying Corps and then served in the Royal Naval Air Service and Royal Air Force during the First World War. In 1921 Sempill led an official military mission to Japan that showcased the latest British aircraft. In subsequent years he continued to aid the Imperial Japanese Navy in developing its Navy Air Service.

However in the 1920s Sempill began giving military secrets to the Japanese. Although his activities were uncovered by British Intelligence, Sempill was not prosecuted for spying and allowed to continue in public life. The decision, which was taken at highest levels of government, was based on several factors. Firstly it would have revealed British successes in decoding Japanese communications and secondly he was part of the British Establishment with family links to the Royal Family.