Microwaves, Nazi Tech, and the US Navy.
1) Nazis discover Microwaves, but also found that microwaved food caused cancer.
>https://rationalwiki.org/wiki/Microwave_oven#The_Nazis_discovered_microwaves.21.5B1.5D
2) Conjecture; Nazis expand to find out what we now know, and discover anti-gravity.
What we know now;
>https://patents.google.com/patent/US10144532B2/en
3) Nazis hire Horton brothers to build an airplane that can cold the triangular shape required for a resonating chamber for microwave anti-gravity.
>https://en.wikipedia.org/wiki/Horten_Ho_229
4) John F. Kennedy, serving in Navy intel finds out from his spies in Germany about the Horton and Microwave anti-gravity, and with this knowledge starts what would be later known as the "Philadelphia Experiment".
5) Nazis send teams to south pole to further the development in secret in case they cannot get it fulling working in time to win the war.
>https://en.wikipedia.org/wiki/New_Swabia
6) Nazis lose war and US gains some of the Horton brothers craft and start testing ASAP. This leads to the sighting in Washington State that coins the name "Saucers", further shaping the dis-info surrounding the craft. Key - "Arnold described them as a series of objects with convex shapes, though he later revealed that one object differed by being crescent-shaped…". Horton signature shape.
7) Nazis leaves Earth and start "Dark Fleet".
8) US Navy leaves Earth and starts the SSP.
9) CIA gets its hands on the tech and makes the TR-3B and more.
10) US Navy dusts off the papers done in WW2, and begins the Advanced Tactical Aircraft (ATA) Program 1983, to combat the growing external Nazi threat to Earth.
>https://en.wikipedia.org/wiki/McDonnell_Douglas_A-12_Avenger_II#ATA_program
11) Now the ships are ready for battle, and the Nazis are ready to invade Earth?
12) I have no clue, but if anyone has been paying attention to the news you know something is up, literally.