Well first off, it was called the "Die Glocke", which is German for "The Bell". The only reason some people call it a ufo is the shape of the object. As well as by no means were the Germans helped by aliens to gain this technology. Honestly, the Germans during WW2 stole money from all around Europe, and were able to finance these technological strives. America since WW2, also has become one of the richest countries, and look at the advances it has made. Therefore, it is no surprise the Germany was able to become so far more advanced.
The Bell was first came to life thanks to a Polish journalist named Igor Witkowski, with his book, The Truth about the Wunderwaffe. Witkowski, who will not tell who gave him the information, claims he got his information from a Polish intelligence contact who claimed to have access to Polish government documents regarding Nazi secret weapons. He believes that The Bell was a anti-gravity and tested at a rig (picture above) located in Poland.
What do I think the rig is? Well first lets look at what The Bell is believed to have looked like.

Some have believed that The Bell was some kind of time machine, and something similar to "The Philadelphia Experiment". However, look at the picture on the left, I do not believe that a time machine would be transported to the outside like that. Leading me to believe that yes it is possible to be a Time Machine, but not the strongest lead.
My strongest theory is that it was a device the breeding of Uranium 233 from Thorium 232. It was a Tokamak like, plasma induction coil for which the electrical giant AEG was awarded highest priority and the code name Charite Anlage. The Project was called "Projekt Thor".
Where was the bell first located and last location?
First it was located inside the Wenceslas mine and above the ground there was a power station with two steam cooling towers. There is speculation that five of these bells existed. At Bissingen in April 1945 the French captured what appeared to be anincomplete Bell device created by the Swiss scientist Dallenbach. In the end, Dr Ronald Richter attempted to recreate the bell in Argentina. However, the Argentinean goverment wanted the bell dismantled.
How The Bell Worked?
This information comes from https://sites.google.com/site/nazibelluncovered/
"vaporised Mercury was spun in a magnetic field to provide excited electrons. Mercury is known to fluoresce easily. Under the influence of an elctromagnetic filed electrons would disassociate from their atomic nucleii and would swirl around the machine much like a doughnut shaped plasma (toroid). As photons colided with free electrons those colision would generate X-rays.
The spinning of these electrons, probably in an evacuated low pressure chamber with just small amounts of mercury vapour, would lead to faster and faster speeds. With each rotation more and more electrons would be stripped from the Mercury perhaps causing double and triple ionisation.
Plasma is an electrically induced state of matter beyond those which we are normally used to, like solids, liquids, or gas. We have all see Plasma. It is present in Lightning."
Prof. Walter Gerlach, a German physicist, wanted to use a photo-energy method for obtaining fissile uranium. Photochemistry relies on the ionization of an intermediate element to create a plasma. In this case using Mercury. X-rays would be generated from the ionized plasma. Sporrenberg referred to use of Beryllium oxide inside the Bell centrifuge. Berlium is known to donate slow neutrons when bombarded by X-rays.
Evidence of the bell?
The image is Nazi research paper captured at Strassburg concerning wartime nuclear projects.
Prof. Walter Gerlach, a German physicist, complained about difficulties assembling the engineers required for his photo-chemistry project.
The above picture is the plane (Ju-290) is to have evacuated the Nazi Bell.
The Nazi's claimed that this device could win the war for them, even when all things seemed to have fallen apart for the Germans. Well, the Germans were the first to have discovered Nuclear Fission. If the project was to be successful, and the Germans would have master Nuclear Weaponry, and with the V2 rockets being capable of reaching New York, we would all be speaking German right now.
This is the real story behind the Nazi Ufo. The website https://sites.google.com/site/nazibelluncovered/ goes into much greater detail then my blog. I simply tried to quickly sum it up.