Military Intelligence (Unit 5) was established during the 1930s. In those days, and especially during World War 2, there were many different units, numbering from 1 to 20. For instance, MI9 had special responsibility to the Royal Family.
But MI5 were the most important unit of all, and dealt with counter espionage in the United Kingdom. Perhaps their finest hour was when they replaced Prime Minister Winston Churchill with an actor, after learning that a crack squad of Nazi soldiers had taken over a village on the east coast. Unfortunately, the real Winston Churchill was misplaced in the confusion, and thus the actor was used for many years afterwards.
MI5 then set up a special section (‘N’ - now defunct) to oversee the development of ‘newtowns’. The history of N branch is shrouded in mystery. No-one is sure who ran it, or what their orders were. One theory is that the motivation for building newtowns was to prevent further war, by creating towns so ghastly that no-one would ever want to invade them. However, this is only speculation.
Other sections were set up to deal with various problems.
Current structure:
| Section | Function |
| A | Industrial Espionage |
| B | CIA |
| C | MI6 |
| D | Counter Espionage |
| E | Under the Counter Espionage |
| F | Counter Terrorism |
| G | Counter Memoirs |
| H | Administration |
| I | Catering |
In recent years, particularly since the collapse of the Soviet Union (well done D branch!) the role of MI5 has changed. We are now fighting organised crime, terrorism and the ever present threat of line dancing.