[2] During World War I, Charles worked in Royal Army Medical Corps, and was promoted to the rank of Captain and 1917, he posted to France, Belgium and later Italy.

[3] Charles returned to Newcastle in City Hospital for Infectious Diseases in 1928, being promoted to medical officer for health in 1932.

[2][3] Charles moved to London in 1944 as Deputy Chief Medical Officer where he assisted with the planning of the National Health Service.

[2] When Charles succeeded Jameson in 1950, he became the first CMO to be appointed to the Home Office as well as the Ministry of Health and Department for Education.

It has been suggested that Charles was kept in his post as CMO due to him being content with the Ministry's weak stance on smoking.