Columbia subject headings:
Fortification--Germany (West)--History--20th century.
Siegfried Line (Germany)
World War, 1939-1945--Germany.
Harvard subject headings:
Fortification--Germany--History--20th century.
Siegfried Line (Germany)
World War, 1939-1945--Engineering and construction.
Princeton subject headings:
Fortification--Germany (West)--History--20th century.
Siegfrieg Line (Germany)
World War, 1939-1945--Germany.