Overview
The chief of the Secret Intelligence Service serves as the head of the Secret Intelligence Service (SIS, also commonly known as MI6), which is part of the United Kingdom intelligence community. The chief is appointed by the foreign secretary, to whom they report directly. Annual reports are also made to the prime minister.
The chief of the Secret Intelligence Service typically signs letters with a "C" in green ink. This originates from the initial used by Captain Sir Mansfield Smith-Cumming, when he signed a letter "C" in green ink. Since then the chief has been known as "C".
History
From 1782 until 1909, British intelligence at the government level was handled directly by the Foreign Office, with the Army and Navy also maintaining their own intelligence branches. By 1909, growing tensions with Germany led the Committee of Imperial Defence to recommend the creation of the Secret Service Bureau to provide organization and leadership to the intelligence-gathering process as well as a layer of insulation from espionage activities for the Foreign Office. A 10 August 1909 letter from the Director of Naval Intelligence, Alexander Bethell, to then-Commander Mansfield Smith-Cumming offered him a "new billet": the opportunity to head the Foreign Section of the new Secret Service Bureau. Cumming was to begin in this role on 1 October 1909, but bureaucratic and funding obstacles delayed the start of his work. His first full day in this capacity was not until 7 October, and even then, he "went to the office and remained all day, but saw no one, nor was there anything to do there."
Cumming's tenure as chief established many of the traditions and trappings of the office. Among the best known of these, he signed documents with the initial "C" in green ink, a custom upheld throughout the history of the service. One tradition that was not maintained was the selection of the Chief from the ranks of the Royal Navy. Although Cumming and his successor Hugh Sinclair both had long Navy careers, in 1939 Army veteran Stewart Menzies was appointed over naval officer (and Churchill's preferred candidate) Gerard Muirhead-Gould. Plans to rotate the selection of Chief among the various branches of military service were considered, but most subsequent Chiefs have been career intelligence officers.
From Wikipedia (CC BY-SA 4.0).