ABOUT US
MI5 originally stood for "Military Intelligence [Department] 5". The Secret Service Bureau (SSB), formed in 1909 to counter the danger to Britain from German espionage, became part of the Directorate of Military Intelligence in 1916. A number of departments existed in this Directorate (see below), and the division of the SSB responsible for counter-espionage within the British Isles (as opposed to overseas) became Department 5, or "MI5". MI5 was renamed the Security Service in 1931, following amalgamation with the Special Section of Scotland Yard. The Service never completely shook off its old name, however, and is still commonly known as MI5 today.
See "What's in a Name?" for more details.
There were a number of departments within the Directorate of Military Intelligence (MI1 through MI19) which dealt with a range of issues. For example, MI1 was responsible for code-breaking, MI2 handled Russian and Scandinavian intelligence, MI3 dealt with the rest of Eastern Europe and MI4 looked after aerial reconnaissance. The responsibilities of these departments were either discontinued or absorbed into The War Office, MI5 and MI6 and, later, GCHQ.
In October 1909, Captain Vernon Kell of the South Staffordshire Regiment and Captain Mansfield Cumming of the Royal Navy jointly established the Secret Service Bureau following a recommendation by the Committee of Imperial Defence, which had been considering the danger from German espionage.
To meet an additional requirement from the Admiralty for information about Germany's new navy, Kell and Cumming decided to divide up their work. Thereafter, Kell, or "K", was responsible for counter-espionage within the British Isles while Cumming, or "C", had responsibility for gathering intelligence overseas. The two divisions became MI5 and MI6 respectively. Whilst the head of MI6 is still referred to as "C" today, the Director General of MI5 has not been known by the soubriquet "K" since the 1940s.
See "Origins" for the full story of how the Security Service was founded.
At the centre of the Service crest, which was approved by the Garter, Principal King of Arms in 1981, is a golden winged sea lion on a blue background which represents our historical association with the three armed services. The colour blue signifies our overseas ties. Surrounding this central emblem are three further symbols: a green cinquefoil, a portcullis and a red rose. The cinquefoil's five petals allude to the "5" in MI5, and the colour green has been associated with intelligence since the First World War.
The portcullis, traditionally a symbol of parliament, relates to the Service's function of upholding parliamentary democracy, and the crown over the top of the portcullis at the top of the crest refers to our status as crown servants. The rose has historical associations with state intelligence work - Sir Francis Walsingham, the head of Queen Elizabeth I's 16th century "intelligencers", used it on his seal. At the bottom of the crest is our motto: "Regnum Defende", meaning "Defend the Realm".