From the preview:
When the Great Rivet Wars became less static and the front lines began to move day to day the large rail guns deployed by the Blight became obsolete. Under the direction of the Iron Chancellor, these guns were refitted with Heavy siege chassis. Although incredibly heavy the Hammer is quite mobile and considered a tremendous asset in breaking allied strong points.
The Gryphon’s Hammer weighs in at 120 tons. The barrel is over 4 meters long. It fires 24 inch shells and is propelled by a 600 hp Dailmur diesel engine.