Columbia subject headings:
Atlantic Wall (France and Belgium)
Fortification--Europe.
Maginot Line (France)
Siegfried Line (Germany)
World War, 1939-1945--Campaigns--Western Front.
Harvard subject headings:
Atlantic Wall (France and Belgium)--History.
Fortification--Europe--History--20th century.
Maginot Line (France)--History.
Siegfried Line (Germany)--History.
World War, 1939-1945--Engineering and construction.
Princeton subject headings:
Atlantic Wall (France and Belgium)--History.
Fortification--Europe--History--20th century.
Maginot Line (France)--History.
Siegfried Line (Germany)--History.
World War, 1939-1945--Engineering and construction.