The Secret Intelligence Service (SIS), commonly known as MI6 (Military Intelligence, Section 6), is the British intelligence agency which supplies the British government with foreign intelligence. The SIS Chief is held accountable to the Foreign Secretary. SIS is bound by the Intelligence Services Act 1994. SIS is frequently referred to by the name MI6 (Military Intelligence, Section 6), a name used as a flag of convenience during the First World War when it was known by many names.[5] The existence of the SIS was not officially acknowledged until 1994. It forms a part of the UK's intelligence machinery alongside GCHQ, MI5 and Defence Intelligence.
In late 2010, the head of the SIS delivered what he said was the first public address by a serving chief of the agency in its then 101-year history. The remarks of Sir John Sawers primarily focused on the relationship between the need for secrecy and the goal of maintaining security within the UK. His remarks acknowledged the tensions caused by secrecy in an era of leaks and pressure for ever-greater disclosure.
Since 1995, the SIS headquarters have been at Vauxhall Cross on the South Bank of the River Thames.
The service derived from the Secret Service Bureau, which was founded in 1909. The Bureau was a joint initiative of the Admiralty and the War Office to control secret intelligence operations in the UK and overseas, particularly concentrating on the activities of the Imperial German government. The bureau was split into naval and army sections which, over time, specialised in foreign espionage and internal counter-espionage activities, respectively. This specialisation was because the Admiralty wanted to know the maritime strength of the Imperial German Navy. This specialisation was formalised before 1914. During the First World War in 1916, the two sections underwent administrative changes so that the foreign section became the Directorate of Military Intelligence Section 6 (MI6), the name by which it is frequently known in popular culture today.
Its first director was Captain Sir George Mansfield Smith-Cumming, who often dropped the Smith in routine communication. He typically signed correspondence with his initial C in green ink. This usage evolved as a code name, and has been adhered to by all subsequent directors of SIS when signing documents to retain anonymity