|Marriage of Sadler and Flora McBain|
© G.A. Wilkins
Donald Harry Sadler (1908-1987), born in Dewsbury Yorkshire, was the son of a master tailor and a school teacher. He went to Trinity College Cambridge with an open Entrance Exhibition in mathematics and various other scholarships. At Cambridge he obtained a BA degree with first class honours in mathematics in 1929, and was awarded his MA degree in 1933. He married Flora Munro McBain (1912-2000), a mathematician and head of the Occultation Section of HMNAO. It was described in the History of the Royal Astronomical Society (vol 2 p157) as the "romance of the decade" .
On the suggestion of Smart (author of Smart's Spherical Astronomy), Sadler was invited by Comrie, who had not long been appointed Superintendent, to consider a post in the Office, and if interested to attend an interview. The job as Temporary Assistant, which Sadler accepted in October 1930, paid £6 per week, and was an un-established temporary post. At that time the office was located at the Royal Naval College, Greenwich where it remained until 1939.
In 1933 Sadler became an established member of staff and was promoted to Deputy Superintendent. Three years later, on the sudden suspension of Comrie, Sadler was appointed Acting Superintendent, with the title as seventh Superintendent of The Nautical Almanac being confirmed on 27th July 1937. The Board of the Admiralty also decided that HMNAO should become a part of the Royal Greenwich Observatory, and Sadler became Chief Assistant to the Astronomer Royal (Harold Spencer Jones).
Sadler successfully concluded several projects initiated by Comire, the new Planetary Co-ordinates 1940-1960, Interpolation and Allied Tables, the first Air Almanac (for the end of 1937), a 16-volume set of Astronomical Navigation Tables (AP1618) and Apparent Places of Fundamental Stars (for 1941).
In 1939 the Office moved to Devonport House for threes months (July-September) before being evacuated to Bath. Mary Croarken  summaries the work during the war:
Unlike the other service ministries, the Admiralty already had a well equipped and knowledgeably staffed computing centre in the form of the Nautical Almanac Office. While before the war the Admiralty had sacked Comrie for taking on outside work, when war broke out the Admiralty recognised that it had an extremely valuable resource which it came under pressure to open up. Donald Sadler, Comrie's successor as Superintendent, began to take on outside work in autumn 1939. In the first two years of the war HM Nautical Almanac Office took on ballistics table work for the Ordnance Board, the Air Ministry and the Ministry of Aircraft Production as well as more specialist one off pieces of research work for various Admiralty research establishments; one example was a calculation involved in mine design. To add to the pressure on HM Nautical Almanac Office its own work had increased. Before the war the computation of star positions had been jointly shared between several countries. The war had terminated those agreements and HM Nautical Almanac Office had now to calculate all its own astronomical data for the annually published Nautical Almanac - now an even more critical publication for navigational purposes. However, it was not until July 1941 that Sadler received an extra member of staff to help cope with the ever increasing work load. Because of Sadler's unique position in running a major computing facility to which many service ministries were applying for help, he could see a need for a large, central computing facility to which all of the armed forces and the scientific civil service could have access. In 1941 he wrote a formal proposal for the creation of just such a facility but the suggestion came to nothing as the ever increasing crisis of computing resource had not yet been recognised by those in power. A suggestion from another quarter to centralise computing within the Admiralty did, however, bear fruit.
Sadler had a most distinguished career. In 1948 he was awarded the Order of the British Empire Medal (OBE); he also received the Thurlow Award of the US Institute of Navigation in the same year. In 1950 he was elected Membre Correspondent du Bureau des Longitude, Paris .
Sadler's flair for organisation was recognised by the International Astronomical Union (IAU), and was appointed its General Secretary during the period 1958-1964. The following is a list of awards and appointments made recognising Sadler's work for the International Astronomical Union (IAU) of which he was General Secretary from 1958 to 1964.
|Year||Internationallly Awarded / Elected|
|1964||Foreign Member of the Sociètè Royale des Sciences de Liège|
|1969||Adion Medal by the International Observatory at Nice|
|1972||Honorary Doctorate by the University of Heidelberg|
|1979||Honorary Member of the US Institute of Navigation|