Interesting fact:

Ever wondered where some of the most famous espionage agencies got their names? Take MI5 and MI6 for example, branches of the British Directorate of Military Intelligence. There were actually a ton of departments that existed prior to these two, along with MI1, which dealt in codes, and MI4, which covered maps. However, as of today, MI5 and MI6 are the only surviving branches. That we know of, at least.