Columbia subject headings:
Harvard subject headings:
Espionage--Germany--History--Sources.
Espionage--Germany--History.
Military intelligence--Germany--History--Sources.
Military intelligence--Germany--History.
Secret service--Germany--History--Sources.
Secret service--Germany--History.
Princeton subject headings:
Espionage--Germany--History--Sources.
Espionage--Germany--History.
Military intelligence--Germany--History--Sources.
Military intelligence--Germany--History.
Secret service--Germany--History--Sources.
Secret service--Germany--History.