Realising that the assistant commissioners' workload was becoming too great, Commissioner Sir
Edward Henry was allowed by the
Police Act 1909 to add a fourth assistant commissioner, who took over some of the duties of the Assistant Commissioner (Executive). The four became known as Assistant Commissioners "A", "B", "C" and "L", heading departments with the same letter designations. Assistant Commissioner "A" in effect acted as Deputy Commissioner until 1931, when a separate Deputy Commissioner was appointed. From 1922 to 1931, Assistant Commissioner "A" was generally known as the Deputy Commissioner. After
World War I, Assistant Commissioner "B" became responsible solely for traffic and lost property, with his other former duties divided between Assistant Commissioners "A" and "L". Assistant Commissioner "L" was responsible for "L" (Legal) Department until its reorganisation in 1931. After 1931, he was renamed Assistant Commissioner "D" and became responsible for policy and planning. By the end of
World War II, Assistant Commissioner "A" (Operations and Administration) was responsible for all uniformed police, including specialist units, except traffic police, which were under Assistant Commissioner "B" (Traffic). Assistant Commissioner "C" (Crime) headed the
Criminal Investigation Department (CID), and Assistant Commissioner "D" (Personnel and Training) was responsible for recruitment, training, welfare, communications and
police dogs. In 1970, Commissioner Sir
John Waldron designated Assistant Commissioner "D" as the senior Assistant Commissioner. As policing became more technical, Assistant Commissioner "B" also became responsible for technical support. ==Reorganisation in the 1980s and 1990s==