Columbia subject headings:
Harvard subject headings:
Atlantic Wall (France and Belgium)--Congresses.
Fortification--Europe--History--20th century--Congresses.
Fortification--Scandinavian Peninsula--History--20th century--Congresses.
World War, 1939-1945--Campaigns--Western Front--Congresses
Princeton subject headings:
Bunkers (Fortification)--Denmark--History--20th century.
Denmark--History--German occupation, 1940-1945.
Fortification--Denmark--History--20th century.
World War, 1939-1945--Denmark.