Schwerer Gustav
German ww2 railway gun, it works with or without rails.
Right driver seat controls the wheels and left controls everything else.
Left seat:
1: Left elevator up /down
2: Right elevator up /down
3: Open hatch on the barrel
4: FIRE!
Reload cannon by placing a 2×2 cardboard square on top of the two bearings and an explosive barrel or something similar attached to it.