MI5 - Security Service

What happened to MI1 - MI4?

MI5 was founded as the Home Section of the Secret Service Bureau. It was part of the War Office for part of the First World War, between 1916 and 1918. During this time it was renamed MI5, referring to its status as the fifth branch of the Directorate of Military Intelligence (see Where does the name "MI5" come from and why is this name still used?). In the Second World War, MI5 was independent of the War Office, though it worked closely with it.

The Old War Office.

There were a number of MI (Military Intelligence) sections within the War Office's Directorate of Military Intelligence during both the First and Second World Wars. There were eventually ten MI sections during the First World War and seventeen by the end of the Second World War. The number of MI sections and their precise functions varied considerably as the demands of the war effort changed.

Few had anything to do with secret intelligence. For instance, MI4 during the First World War was responsible for supplying military maps, while MI9 during the Second World War helped Allied troops to evade and escape from behind enemy lines.

All of these sections, with the exception of our colleagues in the Secret Intelligence Service (MI6), were later discontinued or absorbed into other organisations.

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