Question: 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?

Context paragraphs:
10.5 cm SK L/35: The 10.5 cm SK L/35 (SK - Schnelladekanone (quick-loading cannon) L - Länge (with a 35-caliber long barrel) was a German naval gun developed in the years before World War I that armed a variety of warships of the Imperial German Navy during World War I.  In addition to the Imperial German Navy the 10.5 cm SK L/35 was used by the Royal Netherlands Navy, Ottoman Navy and Spanish Navy.

10.5 cm SK L/45 naval gun: The 10.5 cm SK L/45 ("Schnelladekanone Länge 45", quick-loading cannon with a barrel length of 45 calibers) was a German naval gun that was used in World War I and World War II and was the successor of the older 10.5 cm SK L/40 naval gun.

21 cm SK L/40: The 21 cm Schnelladekanone Länge 40, abbreviated as 21 cm SK L / 40, was a German naval gun developed in the years before World War I that armed a number of the Imperial German Navy's protected and armored cruisers. Later spare guns were adapted to railway guns during World War I and later employed as coastal artillery during World War II.

Amiens Gun: The Amiens Gun is a German 28 cm railway gun (originally mounted in the battleship SMS Hessen) that was captured by the Australian Imperial Force during World War I and returned to Australia as a war trophy.  The 28 cm SK L/40 "Bruno" (SK – "Schnelladekanone" (quick-loading cannon) L – "Länge" (with a 40-calibre barrel)) gun was placed on public display on 26 March 1920 adjacent to the Central railway station, Sydney.  While the gun's carriage was scrapped during the 1960s, the gun barrel remains on display at the Australian War Memorial in Canberra.

Type 3 120 mm 45 caliber naval gun: Type 3 120 mm 45 caliber naval gun was a Japanese naval gun and coast defense gun used on destroyers, submarines and torpedo boats of the Imperial Japanese Navy during World War I and World War II.  The proper title of the gun under the Japanese naval artillery naming system is 12 cm/45 3rd Year Type naval gun.  Other guns using this naming system are the 41 cm/45 3rd Year Type naval gun, 20 cm/50 3rd Year Type naval gun, 15.5 cm/60 3rd Year Type naval gun and the 12.7 cm/50 Type 3 naval gun.

24 cm SK L/40: The 24 cm Schnelladekanone Länge 40, abbreviated as 24 cm SK L/40, was a German naval gun developed in the years before World War I that armed a number of the Imperial German Navy's pre-dreadnought battleships and armored cruisers. Later guns removed from these ships were converted to coastal artillery and were used during World War I and World War II.  The actual bore diameter was 23.8 cm , but the classification system for artillery rounded up to the next highest centimeter.

21 cm SK L/45: 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 and later employed as coastal artillery during World War II.

15 cm SK L/35: The 15 cm Schnelladekanone Länge 35, abbreviated as 15 cm SK L/35, was a German naval gun developed in the years before World War I that armed a variety of warships from different nations.  The navies of Austria-Hungary, China, Denmark, Japan, The Netherlands, The Ottoman Empire, Romania and Spain all used this gun.

24 cm K L/35: The 24 cm K L/35 was a German Naval Gun developed in the years before World War I that armed ships of the Imperial German Navy, Argentine Navy and the Austro-Hungarian Navy.  Guns removed from ships of the Imperial German Navy were modified to perform Coastal Artillery and Railway Artillery roles and saw service in both world wars.  The actual bore diameter was 23.8 cm , but the classification system for artillery rounded up to the next highest centimeter.

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.  Many countries have built railway guns, but the best known are the large Krupp-built pieces used by Germany in World War I and World War II.  Smaller guns were often part of an armoured train.

Supporting paragraphs: 21 cm SK L/45 Railway gun
Answer: wagon