Sir David Petrie (1879–1961) worked in the Indian Police from 1900-1936, serving in a variety of police intelligence roles. He headed the Delhi Intelligence Bureau of the Indian Police and served as the Chairman of the Indian Public Service Commission until 1936. He joined the Army Intelligence Corps after the outbreak of the Second World War.
In 1941 Sir David was asked by Sir John Anderson, the Lord President of the Council, to carry out a review of the Security Service to establish the causes of the difficulties that it was facing. He concluded that the Service had suffered from poor management and planning which had led to organisational breakdown and confusion.
Sir David was put in charge of the Service in April 1941 and immediately carried out a reorganisation that greatly improved its efficiency. He oversaw one of the busiest periods in the Service's history, during which many successful intelligence operations were carried out against Nazi Germany and the Axis countries. He retired from the Service in the spring of 1946.