Basically the trains were used since end of 1800 to carry guns and other weapons. During WW1 special trains were built in order to carry medium to large naval guns by France, Germany, and Italy
Moreover Italian Navy take care to setup mobile coastal defence convoys during ww1 and maintened active these trains for all ww2, when 12 convoys were used. Moreover one train with Flak was given from Nazi Germany as present to Mussolini at that time.
Here is something from WW1: due to the war the build of BB Cristoforo Colombo was stopped and 10 381/40 guns were "available".Two of the were used for the Monitor "Faà di Bruno", one was kept for spare and 7 were installed on train. The convoy were quite simple: the wagon with the gun, a wagon for the ammunitions and a wagon as workshop.
