Columbia subject headings:
Harvard subject headings:
Anti-Nazi movement--Germany--History--20th century.
Espionage, Soviet--Germany--History--20th century.
Intelligence service--Soviet Union--History--20th century.
Military intelligence--Soviet Union--History--20th century.
Rote Kapelle (Resistance group)
Soviet Union--History--German occupation, 1941-1944.
World War, 1939-1945--Secret service--Soviet Union.
Princeton subject headings:
Espionage--Germany--History--20th century.
Espionage--Soviet Union--History--20th century.
World War, 1939-1945--Secret service--Germany.
World War, 1939-1945--Secret service--Soviet Union.