It may be implausible, but I love the concept of the tank army out of nowhere. I’ve seen it in a few cheap thrillers of dubious quality, and if the context allows it, I love it. It’s just a sign that the author simply does not care about those silly things like “logistics”, or “direct plausibility”.
Where I think I love the tank army out of nowhere (again, assuming the right context, which boils down to not taking things too seriously) has to do with my own hang-ups, where I’ve been too focused on “plausibility”. As a literary tool, seeing the tank army out of nowhere without any explanation save for a lame excuse (and sometimes not even that) makes me think “Ok, here’s tanks-this is going to be ridiculous, whether the author intends it or not.”
And I like ridiculousness in my fiction.