I'm not sure there is any law against owning an unarmed tank. But for "dangerous and unusual" weapons themselves, an important case is from 1939 - Miller vs USA. [1] And it's
absurdly weird. Basically the defendant was a thug with a penchant for snitching on everybody.
In his final case, which he also snitched during, he argued that a law he had been charged under (a firearms regulation law) was unconstitutional. The judge who heard his case was very much in favor of the gun control law and had made numerous public statements as such, but he also likely knew that the law was on very shaky constitutional ground, and had been fishing for a test case to advance it. And he found that in Miller.
So he concurred with Miller about the law's unconstitutionality! That resulted in the case being appealed up to the Supreme Court. Conveniently for the state, neither Miller or his defense representation appeared. So it was argued with no defense whatsoever. And Miller was found shot to death shortly thereafter, which wasn't seen as particularly suspicious given his snitching habits. And that case set the ultimate standard that's still appealed to, to this very day.
This is made even more ironic by the fact that the weapon he was being charged for possession of as being 'dangerous and unusual' was just a short barrel shotgun, which was regularly used in the military.
[1] - https://www.law.nyu.edu/sites/default/files/ECM_PRO_060964.p...