Columbia subject headings:
Harvard subject headings:
Cold War
Espionage--Germany--History.
Espionage--History--20th century.
Intelligence service--History--20th century.
Secret service--History--20th century.
Princeton subject headings:
Cold War.
Espionage--Germany (East)--History.
Espionage--Germany (West)--History.
Espionage--History--20th century.
Intelligence service--History--20th century.