This is based on a vehicle mentioned and briefly described in Raven's Flight (they are even mentioned in the sample audio on the site); Corax takes a couple of them, crewed by Iron Warriors, apart. I'd imagine it would be based on a Vindicator type chassis but with the Earthshaker coming out of...
EDIT: Adding in links to the threads from this post to serve as a kind of "contents page".
Terminator Honour Guard Squad
Sabre Tank Hunter
Land Raider Spartan
Thunderstrike Artillery Tank
and now, the original post...
recently I've become a bit bored with the...