Examples include a thwarted operation to overthrow the Bolshevik government as well as more orthodox espionage efforts within early Soviet Russia headed by Captain George Hill.
Smith-Cumming died suddenly at his home on 14 June 1923, shortly before he was due to retire, and was replaced as C by Admiral Sir Hugh "Quex" Sinclair.
Most of its results came from military and commercial intelligence collected through networks in neutral countries, occupied territories, and Russia.
In early 1944 MI6 re-established Section IX, its prewar anti-Soviet section, and Philby took a position there.
He was able to alert the NKVD about all British intelligence on the Soviets—including what the American OSS had shared with the British about the Soviets.
The most significant failure of the service during the war was known as the Venlo incident, named for the Dutch town where much of the operation took place.
Agents of the German army secret service, the Abwehr, and the counter-espionage section of the Sicherheitsdienst (SD), posed as high-ranking officers involved in a plot to depose Hitler.
At this time, the organisation was known in Whitehall by a variety of titles including the Foreign Intelligence Service, the Secret Service, MI1(c), the Special Intelligence Service and even C's organisation.