Columbia subject headings:
Harvard subject headings:
Germany--History--1933-1945.
Hamburger Hochbahn AG--History.
Nazis--Transportation--Germany--Hamburg.
Railroads, Elevated--Germany--Hamburg--History--20th century.
Subways--Germany--Hamburg--History--20th century.
Urban transportation--Germany--Hamburg--History--20th century.
Princeton subject headings:
Hamburger Hochbahn AG--History.
Street-railroads--Germany--Hamburg--History.
Urban transportation--Germany--Hamburg--History.