Columbia subject headings:
North Sea--History.
Norway--History--German occupation, 1940-1945.
World War, 1914-1918--Campaigns--North Sea.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Norway.
Harvard subject headings:
North Sea--History.
Norway--History--German occupation, 1940-1945.
World War, 1939-1945--Campaigns--North Sea.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Norway.
Princeton subject headings:
World War, 1939-1945--Campaigns--Norway.
World War, 1939-1945--Naval operations, German.