On May 31, 2023 (around 6:30 a.m. Japan Standard Time), North Korea launched a satellite. North Korea announced the launch in advance, prompting the Japanese government to deploy Aegis destroyers in advance. The Aegis destroyer is designed to detect and track ballistic missiles and intercept them if they appear to be threatening or landing on Japanese territory itself. When the Japanese government decided to acquire ballistic missile interceptor capability in 2003, the ballistic missile defense concept assumed that a launch would be reported in advance or that clear signs of a launch would be obtained, as in this case. The circumstances in Asia have changed a lot in 20 years.
As North Korea’s ballistic missile development progresses, the frequency of launches, the types of missiles, and the form of launches have varied. Japanese leaders also have to consider the development of hypersonic glide vehicles and cruise missiles. North Korea has also been developing nuclear weapons, conducting its sixth nuclear test in 2017, and it is expected to conduct a seventh test in the next several years.
To defend Japanese territory from attack, the government initially pursued the Aegis Ashore missile defense system, which was expected to protect all of Japan from North Korean ballistic missiles 24 hours a day, 365 days a year. However, the procurement was cancelled and the Japanese government has now responded to North Korea’s nuclear and missile development with a concept centered on the Aegis destroyer. These ships have been upgraded successively since 2007 to have ballistic missile defense capabilities. Japan now has eight ballistic missile-capable ships in its fleet.
The Japanese government is now rethinking its traditional approach to ballistic missile defense, following the decision to purchase and develop longer-range missiles for counter-strike contingencies. Based on the decision to possess a counterstrike capability and three security-related documents prepared by the Japanese government at the end of 2022, it will now exercise deterrence by denial but also punitive deterrence against the North Korean ballistic missile threat.
The Decision to Introduce Aegis Ashore
When the Japanese government first decided to introduce ballistic missile defense in 2003, leaders had the benefit of time: It was known “when, from where, and what type” of North Korean missiles would be launched. For example, once a missile launcher was erected near a North Korean missile launch site and then fueled, Japanese leaders knew that North Korea would then launch that missile within a few days. Also, the only missiles that posed a threat to Japan were the Nodong or the Taepodong, which were in the development stage at that time.
As North Korea’s missile capability gradually progressed, it developed mobile ballistic missiles that could be launched from locations other than missile launch sites. This has made tracking North Korean missiles more difficult and the deployment of defenses more challenging. In 2012, when I was commander of the Fleet Escort Force, we had to deploy Aegis destroyers for more than 70 days in order to counter North Korean ballistic missiles. Since 2016, North Korea has launched more than 30 ballistic missiles a year, and this has resulted in longer range, improved saturation attack capability, improved surprise attack capability, and more diverse launch modes. As a result, Japan’s Aegis destroyers had to be engaged in continuous missions for even longer periods of time.
Japan’s ballistic missile defense concept is to “defend all of Japan with the Aegis [ballistic missile defense] systems and deploy PAC-3s for double defense in key protected areas such as the Tokyo metropolitan area.” This has become difficult to realize with the Aegis, which carries out its missions at sea.
In December 2017, the Japanese government decided to deploy two land-based Aegis Ashore units to maintain a 24/7, 365-day uninterrupted missile defense system over the long term. The government then began local coordination for the deployment of Aegis Ashore in Akita and Yamaguchi prefectures facing the Sea of Japan to protect all of Japan. In my experience, this coordination proved difficult, however, and although Aegis Ashore-related equipment was purchased, the location of its deployment could not be determined. Eventually, in June 2020, two and a half years after the decision to deploy Aegis Ashore, the Japanese government decided to suspend this project.
Alternative Plan of Aegis Ashore
When the Japanese government decided to suspend the deployment of Aegis Ashore in June 2020, Prime Minister Shinzo Abe said, “What should we do to strengthen our deterrence and response capabilities? We will discuss thoroughly what our security strategy should be, firmly establish a new direction, and promptly put it into action.” Thus, Abe put forth the idea of reviewing Japan’s security strategy itself, including ballistic missile defense, and the government began to consider alternatives to Aegis Ashore. As a result, the government decided to build two Aegis-equipped vessels to replace Aegis Ashore in December 2020. It is impossible, however, to realize the ballistic missile defense aim of protecting all of Japan from ballistic missiles 24 hours a day, 365 days a year with two Aegis destroyers deployed at sea. Consequently, the operational requirement of Aegis-equipped destroyers as a replacement for Aegis Ashore could not be determined. More than two years after the suspension of the Aegis Ashore deployment, an appropriation was finally requested in the Fiscal Year 2023 budget to build Aegis-equipped vessels.
Three Security-Related Documents
It took six long years from the decision to deploy Aegis Ashore to the suspension of its deployment and the decision on its replacement. There is no clear indication of how the Japanese government intends to respond to the North Korean ballistic missile threat. Late last year, the Japanese government prepared three security-related documents (the National Security Strategy, the National Defense Strategy, and the Defense Buildup Plan). Prime Minister Fumio Kishida described these documents as “a major shift in Japan’s security policy since World War II.” The major shifts include a significant increase in the defense budget (from 1 percent to 2 percent of GDP by FY2027) and the retention of a counterstrike capability.
As for missile defense, the Defense White Paper states, “The Cabinet has decided to replace Aegis Ashore with two Aegis System Equipped Vessels.” The three documents do not mention the replacement of Aegis Ashore. However, they state that the new Aegis-equipped vessels will be built to improve the integrated air defense missile defense capability. I believe that Japan is rethinking its traditional approach concerning ballistic missile defense.
The first reason for this belief is that the three security-related documents clearly focus on emergency measures, and the second is the decision to possess a counterstrike capability. There are two ways to deter a North Korean ballistic missile attack: deterrence by denial, which involves enhancing ballistic missile defense capabilities, and punitive deterrence, which requires counterstrike capabilities. The National Security Strategy states, “if Japan continues to rely solely upon ballistic missile defenses, it will become increasingly difficult to fully address missile threats with the existing missile defense network alone.” For this reason, according to the new strategy, “the Japanese military needs counterstrike capabilities, which, in the case of missile attacks by an opponent, enable Japan to mount effective counterstrikes against the opponent to prevent further attacks. At the same time, Japanese forces should be defending the island from incoming missiles by means of the missile defense network.”
In the past, Japan has only used denial deterrence and left punitive deterrence to the U.S. military. Japan now will be able to use punitive deterrence at will. Therefore, the response to missiles launched by North Korea in peacetime is based on a missile defense capability to intercept them, along with a counterstrike capability to deter them from causing an emergency. Concerning the integrated air defense missile defense capability, the National Defense Strategy states, “Missile attacks will first be intercepted by missile defense systems. Then, the capability to launch an effective counterattack in the opponent’s territory will be utilized. By having the ability to launch a counterattack, Japan will constrain the opponent’s missile launch, making it easier for missile defense to intercept, which, coupled with missile defense, will deter missile attacks themselves.”
The new Aegis-equipped vessels will be developed by FY2027 as a capability for this purpose. Thus, the new Aegis destroyers are described as a function of the integrated air defense missile defense capability, not a replacement for Aegis Ashore. The Maritime Self-Defense Force is, I believe, trying to develop a system to prepare for emergencies, including the new Aegis-equipped vessels. In addition, the Defense Buildup Plan indicates the goal of a 12-strong Aegis destroyer fleet in ten years. The eight existing Aegis destroyers will be supplemented by four more Aegis-equipped ships, including the two new Aegis-equipped vessels.
Operational Concept of a 12-Aegis Destroyer Fleet
As noted above, Japan’s three security-related documents indicate that the new Aegis destroyers are not a replacement for Aegis Ashore. In addition, based on my experience, it is not feasible to deploy two new Aegis destroyers in two different locations 24 hours a day, 365 days a year during peacetime. Therefore, the Japanese government will have to change its ballistic missile defense concept. Specifically, the Maritime Self-Defense Force’s Aegis destroyers will no longer be always deployed during peacetime to prepare for a North Korean ballistic missile launch. The Aegis destroyers will be deployed according to the situation, taking into consideration the effect of punitive deterrence through its counterstrike capability. Specifically, they will be deployed flexibly in cases where two Aegis ships are deployed to protect all of Japan, one Aegis destroyer is deployed to protect the Tokyo metropolitan area, or no Aegis ships are deployed at all.
The National Defense Strategy states that as a measure for sustainability and resilience, a system to make all Aegis destroyers operational, except for those under repair, will be established as soon as possible. If 25 percent of the Aegis destroyers are being repaired, approximately nine Aegis destroyers can be made operational. With nine Aegis destroyers in an operational state, it would be possible to deploy the ships in two areas on a continuous basis to protect all of Japan in an emergency. In an emergency, such as if China invades Taiwan, it may be necessary to permanently deploy Aegis vessels to two locations in preparation for a North Korean missile attack. In such a case, two Aegis ships could be deployed for a short period of time to respond to North Korean missile attacks, and the remaining seven Aegis ships could be assigned to other missions related to contingencies involving Taiwan,
Conclusion
Almost 20 years have passed since the Japanese government decided to introduce ballistic missile defense capabilities. During this period, North Korea has dramatically advanced its nuclear and ballistic missile capabilities. The Aegis Ashore was expected to protect all of Japan from North Korean ballistic missiles, but it is unclear whether the new Aegis-equipped vessels can do the same. The Japanese government prepared three security-related documents at the end of 2022 and has shifted its focus from “peacetime to gray zone” responses to “emergencies,” increased its defense budget from 1 percent to 2 percent of GDP, and acquired a counterstrike capability. Based on these decisions, it will now exercise not only denial deterrence but also punitive deterrence against the North Korean ballistic missile threat. With this major shift in Japan’s security policy, the ballistic missile defense concept will probably undergo significant changes and the country will no longer commit to maintaining an uninterrupted 24/7 missile defense system over the long term.
Tokuhiro Ikeda is a director of the National Security Institute at Fujitsu Defense & National Security Limited, a former vice admiral, Japan Maritime Self Defense Force, and was a senior fellow at the Harvard University Asia Center (2021-2023).
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