I would be remiss not to mention Gerald Bull, of the 20th century. I had first read of him in the 1960s when he suggested economical mortars using truck springs to hurl shells.

Later on. he was involved with Iran and the Babylon projuct, which while never finished would have been along the lines of the old rail guns. i had read about the Krupp guns in one of the histories of the company and had the impression the first targets were against the French and targeting Paris from Belgian held rails.
Cheers
GC
http://www.thewednesdayreport.com/twr/Gerry_Bull.htm