When I was in Germany their gun control laws were way, way more stringent than ours here, even in my US state and county of residence which themselves are very tough for the US. Regardless, here in the US if these items were not rendered permanently inoperable, they would be classified here as "destructive devices" and an unregistered owner would face a felony conviction and 10 years in prison if convicted. They would also be subject to forfeiture which in the case of this surviving tank is significant.
I do not have any idea what the rules are for legally privately owning a working, modern large bore artillery gun here in the US and do not plan to own one and have to find out. Still, these items, again if not rendered inoperable, are way outside the limits of what Civil War era collectors legally can own, including Civil War era black powder cannons. So I would not make a direct extension of this case to ours. That said, knowledge of local laws is important. Where I live, it is illegal to own any shell having more than an ounce of powder in it, thus presumably rendering most shotgun shells illegal but it also means no ownership of artillery rounds that have yet to be inerted. I think a couple guys are driving Cadillacs with all the inerting work I have given them, but that is a practical reason why I keep my stuff absolutely clean alongside the obvious safety reason as well of course.
For a dull read on more on the rules in the US:
http://www.titleii.com/bardwell/nfa_faqhtml.html
