ROLES Insights Number 2021-05 December 31, 2021

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Prospects for Submarine-Launched Cruise Missiles in the Japan Maritime Self-Defense Force
Number2021-05

December 31, 2021
By Ryo Hinata-Yamaguchi

On December 30, the Yomiuri Shimbun reported that the Japanese government is mulling plans to arm theJapan Maritime Self-Defense Force (JMSDF) submarines with long-range submarine-launched cruise missiles(SLCM) capable of striking ground targets.
The plan is part of Japan’s move to gain the ability to strike enemy bases in case of attacks by the adversary,
which is one of the central debates in the Kishida administration’s planned revision of the current 2018
National Security Strategy and the National Defense Program Guideline.
From the national security viewpoint, the idea of possessing submarine-launched strike capabilities have theirshare of benefits. The foremost advantage comes from the fact that the missiles can be launched in a lessdetectable manner, allowing surprise attacks and second-strike capabilities. The Japanese government isalready working to strengthen and sharpen the strike capabilities of the Japan Self-Defense Force (JSDF),
including the Joint Strike Missile (JSM) for the F-35s, Joint Air-to-Surface Standoff Missile (JASSM) andLong-Range Anti-Ship Missile (LRASM) for the F-15s, upgraded version of Type 12 Surface-to-Ship Missile(SSM), as well as research on hypersonic weapons systems like the Hypersonic Cruise Missile (HCM) and theHyper Velocity Gliding Projectile (HVGP). Thus for Japan, the SLCMs would diversify the JSDF’s strikecapabilities essential for defense and deterrence.
Yet while the reported plan is a promising new direction in Japan’s defense planning, much comes down tohow it is pursued.
First, there are questions regarding the missiles. According to the Yomiuri article, the SLCM underconsideration will be based on the Type 12 SSM, which has a range of approximately 1,000km. While theRCAST Open Laboratory for Emergence Strategies
Research Center for Advanced Science and Technology, the University of Tokyo
4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 JAPANhttps://roles.rcast.u-tokyo.ac.jp/en
office@me.rcast.u-tokyo.ac.jp

ROLES Insights Number 2021-05 December 31, 2021

1,000km range qualifies the missile as a “standoff” asset that is beyond the reach of enemy interceptors, theyfall short of effective strike assets against enemy bases. That said, if Japan seeks to gain truly effective strikecapabilities, it will need to consider acquiring missiles of a much longer range – not only making it go beyond
the “standoff” category but igniting debates on whether the move adheres to the nation’s policies to possess
capabilities “minimum necessary for self-defense.”
Second, there are also questions about the submarines that will launch the missiles. Currently, the JMSDF has
two submarine flotillas that operate the 2,750t Oyashio-class and the 2,900t Soryu-class, and the new 3,000tTaigei-class is expected to enter service from 2022. Yet despite the efforts to upgrade the JMSDF submarine
fleet, there are problems. Above all, the JMSDF submarines are conventional. As a result, they are inferior in
speed to nuclear submarines, making them more vulnerable during strikes – even if Japanese submarines are
known for their extremely quiet nature.
Another problem regarding the JMSDF’s current submarines is that none have vertical launch systems (VLS).
Even though the Oyashio, Soryu, and Taigei-classes can launch SLCMs from its torpedo tubes, the capacity
to accommodate and launch the missiles is nonetheless far limited compared to submarines that have VLS
installed.
Third, there will be costing issues with the new missiles, but more so if Japan decides to construct a new classof submarines suited for strikes. The draft defense budget for the 2022 fiscal year stands at 5.4 trillion yen(47.2 US Dollars). But although Japan’s defense budget has marked the highest record for the last eight
consecutive years, the fiscal constraints are already high, given the shopping list for new capabilities andoperations and maintenance costs. Moreover, human resource shortages are severe in the JSDF – particularlyin the JMSDF where enhancements are most needed to meet the security challenges. Hence the dilemma isthat although there are solid rationales for striking submarines from the national defense viewpoint, the costs
and constraints would be overwhelming.
Given the growing uncertainties in the regional security environment, Japan’s ability to strike enemy bases isessential to defend and deter against the threats the nation faces. That said, the trick is to find the most costeffective means that efficiently uses Japan’s limited resources and assets while also providing maximumeffects.

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Ryo Hinata-Yamaguchi is a Project Assistant Professor at the Research Center for Advanced Science andTechnology at the University of Tokyo and an Adjunct Fellow at the Pacific Forum. Ryo can be followed on
Twitter at @tigerrhy.

RCAST Open Laboratory for Emergence Strategies
Research Center for Advanced Science and Technology, the University of Tokyo
4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 JAPANhttps://roles.rcast.u-tokyo.ac.jp/en
office@me.rcast.u-tokyo.ac.jp