In the aftermath of Judgment Day, we fled to the Exclusion Zone and sought refuge underground. This is what is left of our fallen civilization.

How Codebreaker Elizebeth Friedman Broke Up a Nazi Spy Ring

https://www.smithsonianmag.com/smart-news/new-pbs-film-tells-story-wwii-codebreaker-elizabeth-friedman-180976759/

Codebreaker

https://www.pbs.org/wgbh/americanexperience/films/codebreaker/