Columbia subject headings:
Espionage, British--Baltic States.
Great Britain. MI6.
Soviet Union. Komitet gosudarstvennoĭ bezopasnosti.
Harvard subject headings:
Espionage, British--Baltic States.
Great Britain. MI6.
Soviet Union. Komitet gosudarstvennoĭ bezopasnosti.
Union of Soviet Socialist Republics. Komitet gosudarstvennoı̆ bezopasnosti.
Princeton subject headings: