William Forbes-Sempill, 19th Lord Sempill

William Francis Forbes-Sempill, 19th Lord Sempill, , (24 September 1893 – 30 December 1965) was a Scottish peer and record-breaking air pioneer, who was later shown to have 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.

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 was allowed to continue in public life. He was eventually forced to retire from the Royal Navy in 1941, after being discovered passing on secret material to Tokyo shortly before Japan attacked Pearl Harbor and declared war on the United States and the British Empire.

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, although in November 1907, having studied there for a year, he ran away, eventually making it to Craigievar before being discovered. Following this incident, he was privately tutored. In 1910, Sempill was apprenticed to Rolls-Royce.

Military and civil aviation At the outbreak of war, 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 was appointed one of several deputy directors in the RAF's personnel department with the temporary rank of colonel. He was awarded the Air Force Cross in the 1918 Birthday Honours. Sempill stayed at the Air Ministry until 8 October 1918, when he was seconded to the Ministry of Munitions. On the cessation of hostilities, he became a test pilot, and he retired from military service in 1919. 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.

In early 1931, Sempill was appointed chairman of National Flying Services, the government-subsidised owner and operator of London Air Park, Hanworth. On 22 March 1931, he hosted a visit by members of the Japanese Royal Family and the Japanese Ambassador to Britain. He arranged and hosted a widely publicised visit of the German airship LZ 127 Graf Zeppelin to Hanworth on 18 August 1931. On 2 July 1932, the airship returned as part of a round-Britain tour.

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, 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. However, 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 Japanese intelligence asked Sempill to obtain secret technical information about the prototype of the Blackburn Iris seaplane. In 1925, Sempill accompanied 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 capacity, about the then-secret Blackburn Iris.

On 28 February 1934, he succeeded his father, John Forbes-Sempill, 18th Lord Sempill, as Lord Sempill and Baronet of Craigevar. His wife Eileen, who had accompanied him on many of his air tours, died in July 1935.

Sempill had "an affinity with militarist right-wing regimes". On discovering that Makihara was in custody, Sempill telephoned and then called at Paddington police station to assure the police of Makihara's innocence and character.

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 the Japanese. The Sempill's first daughter, Ann Moira, was born in 1920. Their second daughter, June Mary, was born in 1922, and was killed aged 18 as a result of enemy action on 11 May 1941 – the last day of the Blitz – at 15 Basil Street, London. She had been serving with the WVS Mobile Canteen Service. Six years after his wife's death from tuberculosis in 1935, They had three daughters, Kirstine Elizabeth, Janet Cecilia and Brigid Gabriel who married Jeremy Menuhin.

Sempill converted to Roman Catholicism in the early 1930s. He was also a druid and a Cornish bard.

Later years and death In 1944, Lord Sempill called on the Premier of Nova Scotia, Alexander Stirling MacMillan, in Halifax, and he offered to buy a part of the province. 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. In 1963, he sold Craigievar Castle to the National Trust for Scotland.

He died in Edinburgh on 30 December 1965. His daughter, Ann, inherited the Sempill peerage, as it was one that could be passed to a female heir. However, the baronetcy, which could only be inherited in the male line, passed to his younger sibling, Ewan Forbes, who had been registered at birth and raised as female, but lived as a man, and had his birth re-registered as male. This inheritance was challenged on grounds of sex by a cousin, John Forbes-Sempill, but upheld in the courts.

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. Sempill's motives and activities, as well as accusations of spying, are still a subject of academic debate.

Sempill's 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.

In correspondence of the early 1940s, between Churchill's office, the Attorney General and the Director of Public Prosecutions, it is observed that Sempill had debts and an overdraft in excess of £13,000 (equivalent to £750,000 in 2012).