 Following the outbreak of World War I he returned to the UK, was commissioned as a 2nd Lieutenant in the 1st Battalion, King's Royal Rifle Corps and saw active service on the Western Front in France and Flanders.In 1919 following the end of the war he returned to his previous employ in Ceylon, after serving in the 5th (Reserve) Battalion of the King's Royal Rifle Corps, Banks was promoted to Superintendent of Police (Grade 1) in 1924 and to Deputy Inspector-General in the Criminal Investigation Department in March 1932.Banks was appointed Inspector-General of Police in 1937, after earlier in the year being presented with the King's Police Medal by the Governor of Ceylon Sir Reginald Stubbs in a special ceremony held at Queen’s House, Colombo.