After learning the existence of Doomsday Machine

After learning the existence of Doomsday Machine, the President and his War Room staff begin making plans for how the survivors can continue living underground long enough to repopulate the planet. The phrase “mineshaft gap” is satiric commentary on the “missile gap” which was the term used to describe the difference between how many nuclear missiles the Soviets had at their disposal and how many the US had. The perception that having a greater number of nuclear missiles somehow translated into being a more powerful threat was used to justify and propagandize the arms race between the two superpowers. The satire here was based on transforming the balance of power from the number of catastrophic missiles each country had to the number of underground mines, capable of keeping survivors of those nuclear attacks alive, each country had.