Hitler's Nazi regime created a mind-bending arsenal of super-advanced but unbelievably bizarre "Wunderwaffe" – or "miracle weapons" – in the death throws of World War 2.
The Luftwaffe were building increasingly wacky aircraft – some shaped like discs or with circular wings.
A US Air Force probe concluded these experimental flying machines may be to blame for UFO sightings.
UFO hunters go further – and insist they still lie hidden in an underground base at the South Pole.
WUNDERWAFFE: Adolf Hitler and a selection of some of the so-called Nazi UFOs
FLYING WING: The front section of the Horten Ho 229
This all may sound ridiculously far fetched – until you see the fantastic aircraft Nazi Germany really was making towards the end of the war.
In a fit of terrifying creativity, Nazi scientists created the world's first cruise missile, the first long-range ballistic missile, the first artificial object to reach space, one of the first military helicopters, a space shuttle – and started developing nuclear weapons.
British aeronautical engineer Roy Fedden – who led the mission to examine German expertise and research at the end of WW2 – said: "I have seen enough of their designs and production plans to realise that if they had managed to prolong the war some months longer, we would have been confronted with a set of entirely new and deadly developments in air warfare."
But some of the lesser-known planes bear a striking resemblance to flying saucers.
HORTEN HO 229
Brothers Reimar and Walter Horten built the world's first jet-powered "flying wing" – an aircraft without tail or fuselage.
The Horten Ho 229 was designed to answer Luftwaffe boss Hermann Göring's call for a bomber designs capable of meeting a "3×1000 requirement" – to carry 1,000kg of bombs a distance of 1,000km at a speed of 1,000kmph.
The US military seized the last Horten prototype as part of Operation Paperclip – a secret mission to captured advanced German weapons research to keep it out of Soviet hands.
The design mysteriously reappeared as the revolutionary B-2 "Stealth Bomber".
BOX SET: The US seized the only surviving prototype
MOTHBALLED: It is in storage at the Smithsonian Museum
STEALTH: The Northrop B-2 looks very similar to the Horten Ho 229
Engineer Arthur Sack spent the war trying to perfect an aeroplane with circular wings.
The Sack AS-6 finally became airborne in 1944 – just before the end of the war.
Photographs of the just-plain-weird plane survive – but the prototype mysteriously disappeared when American troops overran the Brandis air base, where it was stored, in April 1945.
AROUND HERE: The Sack AS-6 had circular wings – like a flying saucer
DISC-O: Only photographs survive from the bizarre craft
Eugen Sänger and Irene Bredt designed the Silbervogel spaceplane for the 1942 "Amerika Bomber" mission to attack the mainland US.
The sub-orbital bomber – a precursor to the Space Shuttle – would be shot into space with a rocket booster and then "bounce" off the atmosphere.
The Arado E.555 was another "flying wing" design put forward for the Amerika Bomber mission.
SHUTTLE: The Nazi's Silbervogel space plane
CHALLENGER: The Silbervogel design used the same principle as a Space Shuttle
But perhaps the most revolutionary – and most mystifying – Nazi UFO was Viktor Schauberger's "Repulsine" engine.
The Austrian inventor developed a round turbine engine that could create a vortex and rise straight upwards.
The SS captured Schauberger and made him try to turn the engine into a vertical takeoff aircraft – which looked exactly like a flying saucer.
The prototype crashed – but the research was said to be continued by a shadowy V2 rocket engineer called Dr Heinrich Richard Miethe.
LOOKALIKE: The Repulsine engine looks suspiciously like a UFO
HOAX: This image – supposedly showing a flying saucer – is almost certainly fake
Miethe – whose existence has never been conclusively proved – was said to have worked on several "Flugscheiben" – or "flight disc" – designs during the early 1940s.
The most notorious of these designs was the fabled V7 – which supposedly harnessed high-intensity electrical charges to turn the oxygen in air into an endless fuel supply.
No photographs of the V7 survive, but after the war, German engineer Bruno Schwenteit patented a flying saucer design he claimed was actually constructed during the war.
The Soviets are said to have seized the V7 prototype when they marched into the Breslau air base in western Germany – now Wrocław, Poland.
In 1952, Miethe reportedly told French daily newspaper France-Soir: "If flying saucers exist, it is the V7 which I built in 1944, the engines of which the Russians seized at Breslau."
REAL: Avro Canada's VZ-9 Avrocar was designed for the US Air Force
IN ACTION: An artist's impression of the Avrocar in flight
Miethe is rumoured to have gone on to work for Avro Canada – which designed a real-life flying saucer for the US Air Force.
The VZ-9 Avrocar was a circular jet aircraft with an estimated speed of 1,500 mph.
Interestingly, when Avro Canada announced the project in 1953, German engineer Georg Klein came out and claimed almost exactly the same design was developed under the Third Reich.
He pointed to Miethe's work at Breslau and that of Rudolf Schriever and Klaus Habermohl at Prague – reportedly taken over by Miethe.
The Cold War Avrocar project was shelved in 1961 due to problems with the design.
RUNDFLUGZEUG: Another supposed Nazi UFO
But these are just the Nazi UFOs for which clear proof exists.
Rumours and even photographs (some clearly fakes) of many others – with fanciful "code names', such as "Rundflugzeug", "Feuerball", "Haunebu" and "Andromeda-Gerät" surfaced after the war.
UFOs were first connected with the Nazis during WW2 – when Allied pilots reported fast-moving round glowing objects following their aircraft.
Airmen believed the objects – dubbed "Foo Fighters" – were futuristic Nazi aircraft.
The only other explanation provided has been electrostatic phenomena – like St Elmo's Fire – or light reflecting off ice crystals.
BOTTOMS UP: An underside view of the Rundflugzeug UFO
The first widely-reported UFO sighting in the US was near Mount Rainier, Washington, on June 24, 1947, by Kenneth Arnold.
The similarity of these nine "crescent-shaped" flying objects (wrongly reported as saucer-shaped) to the Horten Ho 229 "flying wing" was not lost on Project Sign – the first official US Air Force UFO investigation.
In 1959, Captain Edward Ruppelt, the first head of Project Blue Book – Project Sign's follow-up investigation – wrote: "When WW2 ended, the Germans had several radical types of aircraft and guided missiles under development.
"The majority were in the most preliminary stages but they were the only known craft that could even approach the performance of objects reported by UFO observers."
In 1952, Professor Giuseppe Belluzzo, an Italian scientist and former member of the Italian Fascist Mussolini regime – which was allied with Nazi Germay – revealed in a newspaper article that "types of flying discs were designed and studied in Germany and Italy as early as 1942".
SIGHTING: A photograph supposedly showing the Haunebu Nazi UFO
More and more reports of Nazi UFOs surfaced.
Perhaps the most intriguing – and far fetched – is the connection between "Die Glocke" – or "The Bell" – and the Kecksburg UFO Incident.
On December 9, 1965, a large, brilliant "fireball" was seen by thousands in at least six US states and Ontario, Canada.
It streaked over Michigan and Ontario – reportedly dropping "hot metal debris" – and caused sonic booms in Pittsburgh.
It was reported as a meteor – but a family claimed to have seen the object crash land in forest near the village of Kecksburg, near Pittsburgh.
Residents reported finding an acorn-shaped object the "size of a small car" in the woodland.
Almost immediately, the US military turned up, closed off the area and removed the mysterious object.
CIGAR: A photograph supposedly showing the Andromeda Nazi UFO
The UFO is almost identical to the mythical Nazi "Wunderwaffe" Die Glocke.
Polish journalist and author Igor Witkowski claims a contact in the Polish intelligence surface showed him Polish government documents related to secret Nazi experimental weapons.
They described a device "made out of a hard, heavy metal" about 9ft wide, 12 to 15ft high and shaped like a large bell.
Die Glocke – reportedly developed in a (real life) giant underground SS facility known as "Der Riese" – supposedly contained two counter-rotating cylinders "filled with a mercury-like substance, violet in colour" called "Xerum 525".
Witkowski claimed when Die Glocke was activated crystals would form in the tissue of any animals within 200metres and plants would decompose.
So, what happened to all these mysterious Nazi UFOs?
The US – under Operation Paperclip – and the USSR seized as much Nazi advanced weapons research as they could when they divided up German after the war.
The Yanks certainly got Horten Ho 229 and much of the V1 and V2 rocket research, while the Russkis apparently made off with the "Repulsine" engine.
Much of it was reborn in the nuclear missiles and advanced aircraft of the Cold War.
And secret trials of the newly acquired kit would certainly explain some of the alien sightings over the past 70 years.
CLAIMED: The Germans planted Nazi flags, claiming New Swabia
But conspiracy theorists have come up with another theory – the Nazis stashed their Fascist flying machines in a subterranean air base at the South Pole.
Nazi Germany sent an expedition to the Antarctic in 1938 and claimed an area – which they named "New Swabia".
The official reasons for the mission were to seek locations for a new whaling station and naval base.
But UFO hunters are convinced they also established an secret HQ in deep underground caverns to continue developing their new "Wunderwaffe".
They claim the Nazis planned to launch lightning strikes from the base with their new toys.
The real tin hat brigade claim they used the flying saucers to establish a Nazi Moon base.
And some doomsayers even believe they are still there – waiting for the right time to launch a new bid for world domination.