Oh..the name's taken from the 19th century novel "the coming race" by some english gentleman
Presumably from latin virilis (manly, powerful)
there's this legend about a secret society in germany during WWII
well in fact several secret societies, one of which is Vril,
IIRC that's the one -according to the legend- trying to discover the forces of telepathy and telekinesis and basically parapsych through the aether of coming futures.
sidenote: the very same novel is also the reason for conspiracy theorists to claim Nazis believed in some weird hollow earth shirts.. (the Vril-ya from the novel lived underground)
Anywhooo;
basically the same as the russians did in the last Indiana Jones movie...
But luckily this is made up as a "secret society" so all information is vague at best, and that's circularly explained by their secrecy.
Another one is the Thule society .. Thule
existed in pre war germany, but lost members faster than you lose money in vegas...
It still was a perfect name for ct's to use here and there; since there are real life traces

unfortunately that was the satanist part of the occult (think hellboy or older Indiana Jones movies

) not the sciency part...
Back to Vril;
Those were the elite of the master race...
"THE" smartest humans on planet earth and generally the universe as we know it.
As the legend goes, some of the members of the vril society where evil mad scientists -geniuses of course- so they 'invented' more than just one anti gravity engine.
One based on Victor Schaumberger's design
an actual 'mad' scientist, who by redesigning log transport channels improved their capacity whilst reducing the amount of water needed... truly ingenius
in short he followed nature's rules of "no straight lines"..
later he flipped and claimed he could do the same with air and magnetic waves in a way that he actually build several anti gravity devices in his lab.. all lost of course.
One replica is left in his son's museum... no anti gravity there though.
Another one was the Thule tachyonator.. a humongous disc of 'unknown alloy' blablabla.
Collecting the sun's Neutrinos (when this theory arose, Neutrinos were the #1 tachyon candidate in science) and magically charge them to generate lift like an ionocraft or something.
The wrong name gives a good hint

Anyway that's in the "documents" for the Haunebu...
And then there was a combination which name I cannot recall.
A similarly huge torus made of an aluminium alloy completely filled with mercury AFAIK.
the inside of course -since it was convenient- friction free based on Schaumberger's work again.
and it's claimed that if there are absolutely no airbubbles trapped and you can rotate
the mercury inside at a certain rate -using electro magnets *cough cough*-
it'll warp the gravity field or rather deflect it to create propulsion.
Sometimes you can tell which engine was used in a Nazi UFO by looking at the bottom..
if it has a large torus sticking out it was the latter, several hemispheres (likely three) the first.
and if it has a rather flat bottom the thule thingy...
Unfortunately, sometimes they depict one and name another so consistency of information is not exactly given... but hey they deal with conspiracies.... so back to circular logic
'sid