The 21 cm Schnelladekanone Länge 45, abbreviated as 21 cm SK L/45 was a German naval gun developed in the years before World War I that armed the armored cruiser SMS Blücher of the Imperial German Navy, during World War I spare guns were converted to railway guns, a railway gun, also called a railroad gun, is a large artillery piece, often surplus naval artillery, mounted on, transported by, and fired from a specially designed railway vehicle, called what?
21 cm SK L/45:  During World War I spare guns were converted to railway guns and later employed as coastal artillery during World War II. Railway gun: A railway gun, also called a railroad gun, is a large artillery piece, often surplus naval artillery, mounted on, transported by, and fired from a specially designed railway wagon.
wagon