Can they make a hearing device or a new kind of ear or something that allows you to switch from being able to hear above or below whatever frequencies you can hear already?

Answer I don't know the principle of operation, but years ago in "Popular Electronics" magazine, there was a construction article for a device that would allow you to hear super-sonic sounds like dog whistles, the sounds that insects make, etc. I think it mixed and shifted frequencies kinda like a super-heterodyne radio receiver does with RF. Like you, I'd like to have such a device. On the other hand, if a device picked up sub-sonic sounds, it would probably just pick up those "boom trucks" that all the young people drive, and in my opinion we can already hear those things from far enough away (about a mile) Supporting idea Industry uses this equipment.

A link is provided, but only as an example of the stuff being considered. No opinion, pro or con, is stated or implied.It's just a window to look through. Note: the stuff is kinda pricey for non-professional acquisition.

T the www and see what else is out there.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.