"The barest atomic research only got started after the turn of the century and atomic weopans research only really got serious during the course of WW2."
I meant theories. Back in that era, did scientists understand, for example, how the sun produces its energy? Not that they had any idea how to go about reproducing this process, but did they have theoretical knowledge of it? That of course is fusion, but was there any theories at the time about the energy that holds atomic particles together (the "strong" force), and that (theoretically) if an atom were split apart, this energy would be released--i.e. fission? I'm not sure when the existence of subatomic particles was first hypothesized, maybe it is in fact more recent than I think. But I would think it would've been long before we actually figured out how to split an atom.
I never read the novel--just saw the original classic movie--so I don't know what kind of weaponry was imagined by Welles as nearly destroying the human race. But in the movie there was an alarm that was sounded that the Morlocks used to lure the Eloi underground, and an "all clear" signal when enough Eloi went underneath--sounds like Welles imagined some weapon that would produce either radiation or some pestulance (or maybe poison gas?), that humans were conditioned to go underground when the sirens sounded.
Just like "warp technology" and other creations of modern science fiction, supposedly based on theoretical knowledge but far from actual implementability....