[rossmum]

The Germans had a variety of railway guns, from what I recall. I've personally seen one of the smaller ones, but both the Schwerer Gustav and its sister gun (Dora, I think?) were apparently disassembled and lost. Both of those were 800mm guns and had a ridiculously large gun crew; they required their own special railway line with several sets of tracks, and the shells were about the size of a man (if not larger). The gun was incredibly unwieldy as you can probably imagine and didn't fire very fast, but it had a mind-boggling range and the shells were capable of wreaking colossal damage. One was used at Sevastopol, can't remember what became of the other.