[@Apollo26]

Yeah. But I would have the knowledge and industry to upgrade and keep them going.

We're talking about them sitting four hundred years in the elements. Let a sword sit in the elements for that long, see if it still able to be used?

Even at our current level IRL - I wouldn't know the first thing on how to operate, check for damage or even get parts to repair a tank. 

Now take that with people, whom haven't likely seen one for centuries. Whom likely lack the knowledge of where and how to check a tank. Not to mention the industrial capacity to even manufacture those parts.

Or what a tank is or is supposed to do?