Columbia subject headings:
Harvard subject headings:
Espionage, German--United States--History--20th century.
World War, 1939-1945--Secret service--Germany.
World War, 1939-1945--Secret service--United States.
Princeton subject headings:
Espionage, German--United States--History--20th century.
World War, 1939-1945--Secret service--Germany.
World War, 1939-1945--Secret service--United States.