For the real winner in the terror stakes you've got to go with the electro-ray tank.
It scares the willies out of me.
Okay, I'll grant that the electro-ray tank packs enough of an electrical wallop to take out a steel cupola and its Archimedean screws make it more than a match for even the the most jellified mud, but given the fact that it is in the process of annihilating the soldiers that are following along behind it, I suspect that it suffers from something of a targeting deficiency.