Columbia subject headings:
Harvard subject headings:
Ruhr (Germany : Region)--History
World War, 1939-1945--Germany--Ruhr (Region)
World War, 1939-1945--Personal narratives, German.
Princeton subject headings:
World War, 1939-1945--Aerial operations.
World War, 1939-1945--Campaigns--Germany--Ruhr (Region).
World War, 1939-1945--Europe--End.