William Forbes - Sempill , 19th Lord Sempill William Francis Forbes - Sempill , 19th Lord Sempill AFC , AFRAeS , ( 24 September 1893 – 30 December 1965 ) 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 . He was eventually forced to retire from the Royal Navy in 1941 after being discovered passing on secret material to Tokyo shortly before Japan declared war in the Pacific . Sempill was known as " Master of Sempill " before succeeding his father to the titles of Lord Sempill and Baronet of Craigevar in 1934 . Early life . Born at the family seat of Craigievar Castle in Aberdeenshire , Sempill was educated at Eton , and then apprenticed to Rolls - Royce in 1910 . He married Eileen Marion Lavery , the daughter of the Irish painter Sir John Lavery , in 1919 , and their daughter Ann Moira was born in 1920 . Military and civil aviation . At the outbreak of World War I , Sempill joined Royal Flying Corps , being granted a probationary commission as a second lieutenant on 15 August 1914 , which was confirmed less than four months later . In the meantime Sempill was appointed to flying duties . The following year , in February , Sempill took up a position as an " experimental officer " at the Central Flying School and he received a promotion to lieutenant in April . Less than four months later he was appointed a flight commander with the temporary rank of captain . In August 1915 , he was appointed to instructional duties . Sempill ' s time at the Central Flying School was not to last as he relinquished his Army commission at the end of the year on being accepted for temporary service in the Royal Naval Air Service . Sempill ' s rapid rise through the ranks continued in the Navy and at the close of 1916 he was promoted to squadron commander . On 1 April 1918 , with the amalgamation of both flying services into the Royal Air Force , Sempill was transferred and appointed one of several deputy directors in the RAF ' s personnel department with the temporary rank of colonel . In June Sempill ' s award of the Air Force Cross was gazetted . Sempill stayed at the Air Ministry until 8 October 1918 when he seconded on loan service to the Ministry of Munitions . On the cessation of hostilities , he became a test pilot and he retired from military service in 1919 . On 4 September 1930 , he set a new record by flying a de Havilland DH . 60 Moth seaplane ( G - AAVB ) 1 , 040 miles non - stop from Brent Reservoir in London to Stockholm , Sweden in 12 hours . On 26 March 1936 he made a record - breaking flight in a BAC Drone ultra - light aircraft ( G - ADPJ ) 570 miles from Croydon Airport direct to Berlin Tempelhof Airport in 11 hours . He flew back a day or so later in 9 hours though he interrupted the flight with a stop at Canterbury , Kent . Japanese spy . Beginnings . In 1920 he led a civilian British deputation of former naval airmen to Japan , - ' the Air Ministry and the Foreign Office saw the prospect for lucrative arms contracts with Japan - to help develop aircraft carriers , and to assist the Japanese navy in setting up its new air base , after the Japanese had bought three Supermarine Channel flying boats . Sempill was well respected within Japanese circles , and received a personal letter from Prime Minister Tomosaburo Kato ( 1922 – 1923 ) , thanking him for his work with the Imperial Japanese Navy , which he described as " almost epoch - making . " With the termination of the Anglo - Japanese Alliance in 1921 , Sempill should have ended close military contact and discussions regarding naval aviation technology and tactics . But on his return to the United Kingdom in 1923 , Sempill kept in contact with the Japanese Foreign Ministry through the Japanese Embassy in London . Suspicion and questioning . In 1925 Sempill led a mission of foreign air officials to the Blackburn Aircraft factory at Brough , East Yorkshire . The Japanese had previously asked questions about aircraft being developed . Sempill later asked the same questions , in his official position , of the then secret Blackburn Iris . The Directorate of Military Intelligence had kept Sempill ' s communication with the Japanese intelligence officer / Naval attaché in London , Captain Teijirō Toyoda , under surveillance from 1922 . This led to the knowledge of Sempill passing classified secret information to the Japanese , which Toyoda indicated in his communication had been paid for . MI5 tapped Sempill ' s phone , and noted his servant was a Japanese naval rating . In March 1926 , Sempill was proposed by the Aviation Ministry be appointed Greece ' s aeronautical adviser . At this point the Directorate of Military Intelligence advised the Foreign Office and the British Embassy in Athens , that Britain could not be seen to endorse Sempill ' s appointment because of his past activities . Sempill was resultantly called into the Foreign Office for an interview . The questions directed to him were to assess his loyalty to the British Government , his attachments to the Japanese , and the amount of information that he had passed to the Japanese . However , during the meeting , the investigating officer could not reveal that the British had broken Japanese codes and were monitoring the Japanese communications systems . However , on the trip to Brough , Sempill had openly talked about the Blackburn Iris on the upward train trip from London with the foreign air officials . This was witnessed by a British Air Ministry civil servant who reported the incident to his management . Using this information , Sempill admitted that he had broken the Official Secrets Act . However a subsequent meeting , chaired by the Secretary of State for Foreign Affairs Austen Chamberlain , decided it was not in the interests of the British government to prosecute Sempill . Firstly Sempill ' s father was then " aide - de - camp " to King George V ; any public trial would be a grave embarrassment to both The Crown and the British Establishment . Secondly a prosecution would have revealed to the Japanese that British Intelligence had cracked the cypher codes of its diplomatic service . Reprieve and inter - war activities . Six years after admitting he had breached the UK ' s Official Secrets Act , Sempill became a technical and business consultant to the Mitsubishi Heavy Industries ; from 1932 to 1936 he represented the Japanese company in Europe . He also became chair and then president of the Royal Aeronautical Society . In this capacity he advised overseas governments , such as Australia , on the creation of their naval air service s . In October 1933 Sempill was seriously injured in an accident while riding as a passenger in the Dymaxion three - wheel car in the United States . Sempill had been invited , in his capacity as an aviation expert , to review the aerodynamic experimental vehicle at Chicago World ' s Fair . But when he was being rushed to an airport to catch a plane to Akron , Ohio to meet the Graf Zeppelin for its return trip from New York to Europe , the Dymaxion overturned , killing the driver . In 1934 he succeeded his father , John Forbes - Sempill , 18th Lord Sempill to the titles of Lord Sempill and Baronet of Craigevar , taking his seat in the House of Lords as a Conservative peer . His wife , who had accompanied him on many of his air tours , died in July 1935 . Sempill had " an affinity with militarist right - wing regimes " . During the 1930s he developed extreme right - wing political opinions and was active in several anti - Semitic organizations such as the Anglo - German Fellowship , the pro - Nazi Link organisation and The Right Club led by Archibald Ramsay . Espionage 1939 - 41 . On the outbreak of war in 1939 , Sempill was given a position in the Department of Air Materiel at the Admiralty . This gave him access to both sensitive and secret information about the latest British aircraft . By June 1941 , MI5 had intercepted messages between London and Mitsubishi and Field Marshal Yamagata ' s Tokyo headquarters indicating payments were being made to Sempill : " In light of the use made of Lord Sempill by our military and naval attaches in London , these payments should continue " . On further investigation , MI5 suspected that Sempill was passing on top secret information about Fleet Air Arm aircraft . The matter was passed to the Attorney General and Director of Public Prosecutions . But again the Attorney General advised against prosecution . On 5 September 1941 , Sempill attended a meeting with the Fifth Sea Lord and given " a strict private warning " . In 1941 , Special Branch arrested a Japanese businessman called Makahara on suspicion of espionage . On discovering that this representative of a large Japanese firm was in custody , Sempill telephoned and then called at Paddington police station to assure the police of Makahara ' s innocence and character . The Japanese man was released after two days . Sempill was also probably passing on detailed information about the British government . In August 1941 , Winston Churchill and President Franklin D . Roosevelt held a meeting in Newfoundland aboard HMS " Prince of Wales " to discuss the military threat posed by Japanese . Soon after communications between the Japanese embassy in London and Tokyo were intercepted by the fledging Bletchley Park code breakers . The decrypted messages were transcripts of the conference notes . When passed to an alarmed Churchill , he called them " pretty accurate stuff " . Three months later , more notes from Churchill ' s personal agenda and inner circle were intercepted as they were being sent by the Japanese Embassy in London to the Foreign Ministry in Tokyo . Privately Churchill concluded with Anthony Eden only two men could be the source of such leaks : Commander McGrath or Lord Sempill . On 9 October 1941 , a signed note from Churchill says : " Clear him out while time remains . " The following week the Admiralty told Sempill he must either resign or be fired . However after Sempill made an official protest , Churchill backtracked . The Prime Minister told the Admiralty : " I had not contemplated Lord Sempill being required to resign his commission , but only to be employed elsewhere in the Admiralty . " A subsequent note from Churchill ' s aide Desmond Morton , dated 17 October 1941 , outlined the new position : " The First Sea Lord . . . proposes to offer him a post in the North of Scotland . I have suggested to Lord Swinton that MI5 should be informed in due course so they may take any precautions necessary . " On 13 December 1941 , six days after the attack on Pearl Harbor , Sempill ' s office was raided . A search revealed various secret documents that he should have handed back to the Admiralty over three weeks earlier . Two days later Sempill was discovered making phone calls to the Japanese Embassy . Despite the evidence of treason in wartime ( see Treachery Act 1940 ) , no arrest or prosecution was ordered ; Sempill agreed to retire from public office . Later years . In 1956 the Swedish government awarded him the Order of the Polar Star . At various times he was president of the British Gliding Association and of the Institute of Advanced Motorists . He died on 30 December 1965 . On his death , his titles were split ; his daughter , Ann , inherited the lordship of parliament , as this title was able to be passed down the female line ; the baronetcy passed to his younger brother , Ewan . Legacy . It was not until the release of intelligence records by the Public Record Office in 1998 and 2002 that Sempill ' s activities as a spy during the war and in the 1920s respectively became common knowledge . However his motives remain unclear . The National Archives states that " on the evidence of these [ 1920s ] files " , Sempill ' s activities on behalf of the militaristic Japanese and Fascist contacts were less from any desire to help the enemy but more motivated by his own impetuous character , obstinacy , and flawed judgement . However various correspondence in the early 1940s between Churchill ' s office , the Attorney General and the Director of Public Prosecutions , it is noted that Sempill had debts and an overdraft in excess of £13 , 000 ( equivalent to £750 , 000 in 2012 ) .