North Korea's Two Ballistic Missiles Highlight Japan's Aegis Defense Blind Spots

On September 20, North Korea launched two projectiles believed to be ballistic missiles from its eastern coast. According to announcements from the South Korean military and the Japanese government, as well as reports from Reuters and the Japan Times, the launches occurred approximately three hours apart, and both reportedly fell outside Japan's Exclusive Economic Zone (EEZ). While no damage has been confirmed, it is possible that this was not a single act of intimidation, but rather a practical test that continuously pressures monitoring, tracking, and political decision-making.

The Low Number of Two Missiles

If they were short-range ballistic missiles, their range may not necessarily be sufficient to directly attack the Japanese archipelago. However, the issue in defense operations is not solely about the length of the range. If two missiles are launched at different times, the sensor networks of Japan, the U.S., and South Korea must determine whether it is the same attack or if there will be additional launches, while integrating information from naval vessels and aircraft.

The Japan Maritime Self-Defense Force's Aegis destroyers are central to ballistic missile defense. The concept of combining upper-tier interception with SM-3 and ground-based PAC-3 is solid, but it does not mechanically intercept all projectiles. If the impact points are outside the EEZ and the flight paths do not pass through Japanese territory, the legal and operational judgments for interception become more complicated.

The Effectiveness of Japan-U.S.-South Korea Cooperation

This launch occurred shortly after Japanese Defense Minister Koizumi and U.S. Secretary of Defense Hagel agreed to strengthen security cooperation in September. There is a framework for sharing missile warning data among Japan, the U.S., and South Korea, but the speed of sharing and decision-making is not the same. Even if U.S. military satellites and maritime sensors detect signs early, it is a separate issue as to which information Japan decides to disclose to the public and at what stage the Self-Defense Forces will be put on high alert.

Moreover, North Korea's launches are often linked to U.S.-South Korea joint exercises and pressure on the United States. For Japan, it is not about automating involvement in a crisis on the Korean Peninsula, but rather about clearly defining the boundaries of limited missions, including the protection of SLOCs (Sea Lines of Communication) and U.S. forces stationed in Japan, from peacetime.

Overlooked Burdens

Ballistic missile defense requires deploying destroyers at sea and placing crew members on long hours of alert duty. Even if the two launches did not require interception, the detection, tracking, communication, and command systems are still operational. If launches are repeated, the issue shifts from the stock of interceptors to the operational rate of the destroyers and the fatigue of the crew members.

In the author's view, what these two launches demonstrated was not the performance of North Korea's new weapons, but rather Japan's defense structure that imposes burdens even when it is "not shot at."

Sources

• Reuters "North Korea Launches Two Ballistic Missiles Off Its Eastern Coast" September 20, 2026
• The Japan Times "North Korea Fires Off Two Ballistic Missiles" September 20, 2026
• nippon.com "N. Korea Fires 2 Ballistic Missiles toward Sea of Japan" September 20, 2026
• Ministry of Defense of Japan Related Materials on Japan-U.S. Security Cooperation