Big Guns

In a lot of the footage from WWII, particularly scenes of the stree fighting in Berlin, I have seen these HUGE Soviet tracked artillery pieces. I am not sure of the caliber or the nomenclature, but I am sure of one thing - they are pretty cool looking guns. So, my question to you goes something like this: what kind of guns are they and does anyone make a kit of them?

Thanks in advance . You guys rock.