Columbia subject headings:
Harvard subject headings:
Fortification--Alps, Western--History--20th century.
Fortification--Germany--Bavaria--History--20th century.
World War, 1939-1945--Alps, Western.
Princeton subject headings:
Fortification--Alps, Western--History--20th century.
Fortification--Germany--Bavaria--History--20th century.
World War, 1939-1945--Alps, Western.