[quote=@Willy Vereb]
I don't think sticking to the 1950s would work anyways.
This is a post-apocalyptic game or at least in a sense that civilization was destroyed once. Developments don't follow the same route here, at best be close.
Secondly it has steampunk/dieselpunk elements in it. These genres have the typical style of allowing impossibly difficult technologies at the time to become simple and commonplace. In this sense 1950s + dieselpunk means you might as well call it the 70s if not even more advanced in certain things.

So yeah, I feel we shouldn't feel too pressured with the 1950s claim. Just make whatever sounds good yet for the layman might make sense to be developed earlier. The realities of technology and engineering are far less optimistic.
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Saying that, you are quite correct. Development will be very different, more advanced even, perhaps a more proper term, such as "Retro Sci-fi" should be used.

Edit: As for WMD's, pretty much gone.