Columbia subject headings:
Harvard subject headings:
Espionage, American--Germany--History--20th century.
Espionage, German--United States--History--20th century.
Germany--Foreign relations--United States.
Intelligence service--United States--History--20th century
United States--Foreign relations--Germany.
Princeton subject headings:
Espionage, American--Germany--History--20th century.
Espionage, American--Germany--History--21st century.
Germany--Foreign relations--United States.
Intelligence service--United States--History--20th century.
Intelligence service--United States--History--21st century.
United States--Foreign relations--Germany.