He knew about radioactivity; fission was theorized well before it was discovered, and his circle of sf/fantasy nerds was precisely the sort which would both kno

He knew about radioactivity; fission was theorized well before it was discovered, and his circle of sf/fantasy nerds was precisely the sort which would both know about what was then still a relatively obscure branch of physics, and contemplate at length its possible implications. It sounds like you're fumbling toward the question of what Lovecraft would've made of Hiroshima and Nagasaki. Obviously there's no way to know for certain, but I think Charlie Stross has come as close as anyone could in his short "A Colder War", which is freely available online and quite engaging.