Divisional detective inspector (DDI), also known as first class detective inspector, was a rank in the Criminal Investigation Department of London's Metropolitan Police, equivalent to sub-divisional inspector in the uniformed branch.
In the late 19th century, divisional detective inspectors were appointed to local police forces for the first time.
[1] The DDI was in charge of the CID in each police division.
He was largely autonomous on his "patch", answering only to the divisional superintendent and only calling in support from Scotland Yard for very serious crimes such as murder.
The rank was discontinued in 1949, when it was regraded to detective chief inspector.