Hi, I had posted this awhile back on a military train model facebook page but thought I would put it here as well (from a modelers reference perspective).
Cannonissimo Ansaldo à glissement. Took a few hours and made a basic 3D model of an older concept drawing that was found on-line just to see what it may have looked like. This Italian railway design was about twice the size of the Ansaldo 381/40. It followed a similar path that the Germans took in WWI for developing super long range artillery (i.e. Paris Gun) in that they took an older 381mm gun and added 203/210mm extensions. Studies of this concept continued pre-war and in 1939 it appears that the Italians actually transformed two barrels.
Just for fun I also did a graphic comparing the Cannonissimo Ansaldo à glissement overall size to the German 28cm K5 K (E).
Regards