Cerberus Heavy Tank Destroyer
The Cerberus Heavy Tank Destroyer is a super-heavy tank used by the Space Marine Legions during the Great Crusade and Horus Heresy. It is built with the chassis of the Spartan Assault Tank, but instead of twenty-five Marines, it carries a twin-linked Neutron Laser (the same weapon as the Valdor Tank Hunter) and the attendant arc reactor and radiation shielding -- in fact, the extra structure makes it even tougher than the Spartan.
Apparently, the Mechanicus went to a lot of trouble to get the plans for the neutron laser -- they had to recover wreckage "at great cost" from a battlefield dating to the Dark Age of Technology in the Hyades system (a star cluster of some significance to the Cthulhu Mythos, by the way) and reverse-engineer the neutron laser from that. Still, it did provide an alternative to the bulkier turbo-laser weapons, with the "bonus" of risking backlash to the vehicle if the beam bounces off the target.