There has been much talk lately in Japan about beefing up its missile defense system as North Korea, after conducting five nuclear weapons tests, keeps up its ballistic missile program, including firing four missiles simultaneously into the Sea of Japan in March. Yet given that the missile defense system was introduced in the first place as a deterrent against North Korea, it is doubtful whether the system will be effective now that Pyongyang's nuclear and missile programs appear to have made such great strides and the rogue behavior of Kim Jong Un seems as unchecked as ever.
There is no such thing as a foolproof system to strike down incoming missiles. Attempts to pursue that by beefing up the missile defense system will push up defense spending endlessly. The only alternative may be to make the Self-Defense Forces capable of carrying out pre-emptive attacks on North Korean missile bases. But the government is hesitant to take such action, and relies on the offensive capability of the U.S. military. The increased tensions between Washington and Pyongyang since President Donald Trump took office in the United States sheds light on inherent shortcomings of the missile defense system.
Japan's system to combat missile attacks is made up of two stages. In the first stage, naval vessels equipped with the Aegis system cover the entire country, armed with the RIM-161 Standard Missile 3 (SM-3), which is designed to intercept incoming ballistic missiles in outer space. If that fails, the ground-to-air MIM-104 Patriot (PAC-3) is designed to shoot down the missiles at an altitude of 15 to 20 km.