Dame Katherine Jane Trefusis Forbes, Lady Watson-Watt, DBE (1899 –1971) became the first director of the British Women's Auxiliary Air Force (WAAF) in 1939. The youngest of six children of Edmund Batten Forbes (1847–1924), a civil engineer, and his wife, Charlotte Catherine Agnes (Wauchope), Trefusis Forbes was born in Chile where her father, the son of James David Forbes, eminent physicist, and glaciologist, was building the railroad from the coast to the interior. Her grandfather James David Forbes FRS FRSE FGS (1809–1868), a Scottish physicist and glaciologist, was the fourth son of Sir William Forbes of Pitsligo, 7th Baronet (1773–1828).

In 1916, at the height of the First World War, she left school and volunteered for the Women’s Volunteer Reserve. She first served as a private and a driver, and later received her commission as a second Lieutenant. In 1936, Forbes assisted in launching the Emergency Service, to train women to be prepared in case of war. Forbes was appointed Chief Instructor of the Auxiliary Territorial Service School of Instruction in 1938. Three months before the beginning of the Second World War, she was appointed as Director of the WAAF. By September 1939, the force consisted of 1,500 women and by 1943 its ranks had swelled to 175,000. In October 1943, she toured Canada to assess the Women's Division of the Royal Canadian Air Force (RCAF). She also toured India to investigate the possibility of employing women in the South East Asia Command.

In January 1944, Forbes was appointed a Dame Commander of the Order of the British Empire (DBE). She had always been known by her second name, Jane, but on discovering that it would cost her a half crown to change her first name in order to become Dame Jane she decided that she would become Dame Katherine. After the war, she served on numerous charitable and advisory bodies – particularly ones concerned with ex-forces personnel, disabled people and housing.

Forbes inherited "The Observatory" in Pitlochry in 1936, upon the death of her uncle, the physicist George Forbes. The Observatory was built in about 1906 by Professor George Forbes, an outstanding scientist, inventor and engineer. Early in the war, she allowed the house to be used as a place for senior militarily personnel to have a few days respite. After the war, she added additional bedrooms, a bathroom and a kitchen.

In 1966, at the age of 67, Forbes married Sir Robert Watson-Watt, an inventor of radar in 1966. They lived in "The Observatory." Lady Watson-Watt died in 1971 in London, aged 72, after suffering a second heart attack. Her husband died two years later. Both are interred in the churchyard of the Episcopal Church of the Holy Trinity at Pitlochry.