TOKYO, Aug. 22 -- When parts of the Terminal High Altitude Area Defence system were shipped out of South Korea last month for use against Iran, the move did not make the front pages in Seoul or Tokyo. It should have.

THAAD was built for one purpose: intercepting North Korean ballistic missiles in their terminal phase. Three days after the Ulchi Freedom Shield exercises ended a day early this week, North Korea fired more than ten KN-25 ballistic missiles into the East Sea. The sequence - THAAD partially stripped, drills shortened, ten missiles launched - was not coincidental. Kim Yo-jong, the leader's sister and the sharpest voice in North Korea's external messaging, called the drill reduction "an evident disaster." She may be the only on...