Nuclear terror became part of American life, thanks to a purposeful effort by the government to prepare the country for the worst. The Federal Civil Defense Administration advised citizens to build bomb shelters in their backyards and keep clean homes so there would be less clutter to ignite in a nuclear blast. The film “Duck and Cover,” released in 1951, encouraged schoolchildren to act like animated turtles and hide under a makeshift shell — “a table or desk or anything else close by” — if nukes hit. By the 1960s, yellow-and-black signs for fallout shelters dotted American cities. The specter...