It might have been too late in 1939 when a lot of scientists had already left, but it might be very useful to focus on nuclear weapons if you go back a little further.

Germany had the relevant knowledge at the time, and the Manhattan project took just 4 years, so it seems conceivable that Germany could've been nuked other countries into surrendering before those countries got nuclear weapons of their own.

It might turn into a really long guerilla war against very angry populations though...

It might have been too late in 1939 when a lot of scientists had already left, but it might be very useful to focus on nuclear weapons if you go back a little further.

Germany had the relevant knowledge at the time, and the Manhattan project took just 4 years, so it seems conceivable that Germany could've nuked other countries into surrendering before those countries got nuclear weapons of their own.

It might turn into a really long guerilla war against very angry populations though...