Today, Kim Jang-soo, South Korea’s new national security director, said North Korea may fire off a missile as soon as Wednesday. The launch will undoubtedly be a test of an intermediate-range missile, not an attack. North Korea last week moved two missiles, which were subsequently loaded onto mobile launchers, to its east coast. Many expect the missiles, which have been subsequently moved to hidden locations, will be fired in trajectories arcing over Japan. ... The KN-08 sits on an eight-axle mobile vehicle—a transporter-erector-launcher in military lingo—that can hide and shoot, so America’s costly missile defense system is considered necessary because...