In 1919, he moved back to Liverpool to work on
tidal analysis at the newly founded Tidal Institute, which Proudman had persuaded
Charles Booth of Liverpool, and Sir Alfred Booth to sponsor. It was housed in the University Physics Building. With a grant, they could hire an assistant computer, a member of Doodson's staff in London, and buy a desk calculator. He analyzed observations of tides at
Newlyn. This was the first development of the
tide-generating force to be carried out in harmonic form: Doodson distinguished 388 tidal frequencies. Doodson's analysis of 1921 was based on the then-latest
lunar theory of
Ernest William Brown. In 1923, he produced a first
tide table with predictions for 1924, which was used in Liverpool port. He also started to calculate the direction of
cotidal lines and created charts. In 1924, he studied the effects of wind and atmospheric pressure on tides. Portugal and Japan ordered a machine in 1923, Brazil in 1927, made by Kelvin, Bottomley & Baird. Only in 1929 the Tidal Institute bought a 1906 A Légé &Co for itself. As the
Allies prepared the invasion of Nazi-occupied France, they wanted to land at first light when it was
low tide, so hidden obstacles could be seen. Doodson was enlisted to work out the tidal patterns using his mechanised calculators. His calculations revealed that 5–7 June 1944 would provide the best combination of full moon and ideal tidal conditions and
D-Day duly took place on 6 June 1944. By 1943, the staff at Liverpool Tidal Institute had been reduced from 15 to Doodson and six young women. They also did "nighttime fire watch on the roof in tin helmets and trench coats and carrying buckets of water in case an incendiary bomb hit the observatory".
1945–1960 In 1945 Doodson became the Director of the Observatory until his retirement in 1960. His work became increasingly international. Starting in 1948 he became involved in work for
International Union of Geodesy and Geophysics. In 1954, he was made Chairman of the Finance committee. In 1948, he also became the Secretary of the International Association of Physical Oceanography (now the
International Association for the Physical Sciences of the Oceans), which collected monthly and annual mean values of sea-levels from all countries. In 1957, he attended a conference by the
International Hydrographic Bureau and became involved in the financing and production of
bathymetric charts. ==Personal life and death==