This paper is part of a collection, "Missile Defense, Extended Deterrence, and Nonproliferation in the 21st Century - Collected Papers."
The United States and Japan are jointly developing and deploying an integrated advanced regional missile defense system meant to counter threats from North Korea. North Korea possesses a large and diversified arsenal of short- and medium-range missiles that could strike Japanese cities and military bases in the event of a crisis and cause measurable damage. The missile defense system currently in place provides strong kinematic defensive coverage over Japanese territory. However, in general, the offense enjoys a strong cost advantage. It is impractical to deploy as many defensive interceptors as there are offensive missiles, which, in turn, limits the efficiency of missile defenses. It should be understood that regional missile defenses in the Asia-Pacific are neither capable nor expected to provide 100% defense. Rather, their goal is to provide sufficient capability to bolster deterrence and, should deterrence fail, to provide enough defense in the initial stages of a crisis to protect vital military assets. Additionally, U.S. and Japanese forces apparently also need to develop a better command and control architecture to operate the Asia-Pacific regional missile defense system. Finally, while the system is meant to defend only against regional threats, China has argued that the system might in the future be able to intercept Chinese ICBMs, thereby diluting its strategic deterrent against the United States. Maintaining effective defenses against North Korea while reassuring China will be one of the major challenges the U.S. and Japan face in their missile defense endeavor.