Columbia subject headings:
Gibraltar, Strait of--History.
Gibraltar--History.
Spain--History--Civil War, 1936-1939--Secret service.
World War, 1939-1945--Secret service.
Harvard subject headings:
Espionage--Gibraltar--History--20th century.
Gibraltar--History--20th century.
Spain--History--Civil War, 1936-1939--Secret service.
World War, 1939-1945--Secret service--Gibraltar.
World War, 1939-1945--Sectret service--Gibraltar.
Princeton subject headings: