Photo: World of Tanks
Armored trains - a symbol of military might of the turn of the 20th century - are impractical, easily sabotaged, and expensive to operate. But they sure look menacingly cool! Take, for example, this humongous railway gun TM-3-12 which used a gun from a battleship mounted on a train chassis.
Dark Roasted Blend has a nifty gallery of this and many other examples of armored train: Link - Thanks Avi!