America's Doomsday plan. It's the government's ultimate playbook, with a strategy for even the darkest hours - developed when Cold War tensions were high, but never used until 9/11. We'll fly an E4-B - the president's command, control and communications center for times of national catastrophe; go inside the secret bunker used by government officials on September 11; and witness how the luxurious Greenbrier Resort became a critical, top secret congressional bunker..