What is the motto of the British Secret Intelligence Service (SIS), commonly known as MI6?

The Secret Intelligence Service (SIS), commonly known as MI6 (Military Intelligence, Section 6), is the foreign intelligence agency of the British government. The motto of the MI6 is: ‘Semper Occultus’ (Always Secret). The SIS Chief is held accountable to the Foreign Secretary. SIS is bound by the Intelligence Services Act 1994. The name MI6 was used as a flag of convenience during the First World War when it was known by many names. 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.

MI5 motto is: Regnum Defende (Defence of the Realm).

SAS (Special Air Service) motto is: Who Dares Wins.

SBS (Special Boat Service) motto is: By strength and guile.