During the Cold War, the IRS was most eager to figure out how to resume normal operations immediately after an apocalypse scenario. So in 1989, they updated their employee manual with a new chapter entitled "National Emergency Operations," which specified that any and all employees of the IRS, from accountants to janitors, could be reassigned as wasteland tax collectors in the event of an apocalypse, to ensure you're paying your dues within 30 days of our world going full Fallout.
The U.S. Postal Service also had a nuclear apocalypse plan dating all the way back to the '50s, and it was better than the one Kevin Costner came up with. Revised again in the '80s, the USPS Emergency Planning Manual instructed postal employees on how to check mail for radiation before processing, and in the event of a full-scale invasion, to burn all the stamps so that they wouldn't fall into enemy hands. Our vicious, stamp-collecting enemies.
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The Reds aren't winning this game of capture the flag.
The USPS also stockpiled a massive number of change-of-address forms in case of an emergency displacement of the population, so citizens could still get jam-of-the-month deliveries in their new residence, hiding in the burned-out husk of a 7-Eleven. In 1982, Congress called on the USPS to defend the efficacy of the plan, questioning the necessity of a postal service when there's not many people "left to read or write letters after the nuclear bombs explode." To which the United States Postal Service replied: "But those that are will get their mail."