The single largest cannon ever built and used in history. Designed by Krupp Industries it was used during WWII by the Nazi's only against the Russians.
The Scwerer
Gustav is classified as a Supercannon, measuring at a whoping 800mm Calibur, it could only be transported on a double set of rail tracks (also making it a railway
gun).
It could punch through 15 meters of Concrete and 5 meters of solid
metal armor. Unfortunately it was destroyed near the end of the
war to prevent capture. One of its' shells is on display in a Polish war museam.
A second
gun "Dora" was also built but dismantled, and a third was planned by never started.