"After North Korea abandoned a goal of peaceful reunification with Seoul, Kim Jong Un said he will annihilate South Korea and the U.S. if provoked. As tensions on the Korean Peninsula continue to soar, there are increasing concerns that Pyongyang could launch a surprise attack at any moment. "WSJ’s Timothy Martin goes inside Command Post Tango, an underground bunker complex outside of Seoul, where operations of U.S. and South Korean forces would be centralized during a war with the Kim Jong Un regime."