So there has been this fantastically superior technology for nearly 100 years and no military in the world has developed and used it?
Read the book to find out. The technology was advanced in WW2 by the Germans [who were, after all, building on the concepts generated by Ludwig Prandtl and Oscar Schrenk], and we won the war & gained all that war booty.
2 years later we see experimental craft crashing near military bases. That is consistent with a military program, and extremely INconsistent with superduperAdvanced aliens flying at superLUminal speeds.
The 1890s flap of UFOs supposedly marked them at flying the remarkable speed of 200MPH. Would 200MPH be a sign of alien technology TODAY? Nope. How about 4000MPH in 1952, would such a speed be a sign TODAY that they’re from alien worlds? Nope.
