These were the largest self propelled vehicles to be used in World War II. Development of the 60cm model started in 1937 and was finished in 1939. These were intended to be used against the Maginot Line fortifications.
To transport the Mörser's long distance special railcars were made that suspended the Mörser between them while being transported.
The Mörsers could be partially disassembled and transported by specially created trailers.
Starting in 1942 a few of the Mörser's had their 60cm mortar replaced by a 54cm howitzer to increase mobility. The barrels were left interchangeable.
A Munitionspanzer IV was used to transport the very large ammunition and had a crane to lift the rounds into the loading tray of the gun.