A Stupa.
Or timemachine.
We will first look into something that happened 20 years after the war, on 9th December 1965, in Kecksburg. Thousands of people saw a fireball dropping metal debris and starting fires. Eyewitnesses reported an unidentified flying object which crashed into the Kecksburg woods. They claimed that the mysterious object had the shape of an acorn, similar to the Nazi Bell. Of course, the US military came very fast, ordered people leave the area and took the crashed craft. The next day newspapers said that finally, it was a mid-sized meteor.
https://yourtimetravelexperience.com/the-nazi-bell-time-machine
So did the US Military take it?
And what is it, and how much is it developed by now?