CAwriter wrote:

During WW II, my father was a Navy communications officer and SW DXer
at home.

How can I find out how many SW transmitters there were during WW II,
in the US and worldwide?

How many are there now?

You might get some kind of idea as to how many there are now by going to this
site:

http://www.tdp.info/

dxAce
Michigan
USA