This sounds incredible, but I've managed to tap into the Chaos TL's Weltsystem, just like Max a few years ago !
I went to a German militaria fansite and found some fan art of various Walzen from the TL's version of WWI.
Here's one - but it seems to be some sort of artillery modification, probably something like the Gun Carrier Mk I from OTL.
OOC: Actually a piece of concept art from the Half Life 2
mod Iron Grip : The Opression
, with some text added by me.
It's as close as it gets to the Chaos TL's description of its early tanks : "a big armored vehicle, driven by steam - essentially a crossbreed between a locomotive and an OTL WW1 tank".