ROK-Japan-U.S. Anti-Submarine Warfare Cooperation: An Urgent Priority

The Republic of Korea (ROK), Japan, and the U.S. are facing an increasingly dangerous regional environment in Northeast Asia.  The Democratic People’s Republic of Korea (DPRK) continues to behave erratically and provocatively, strengthening its nuclear arsenal, improving its missile capabilities, and carrying out assassinations overseas.  Of particular concern to naval planners, the DPRK continues to operate a large fleet of submarines and is aggressively pursuing the ability to field submarine-launched ballistic missiles (SLBMs). Given these developments, we recommend the ROK, Japan, and the U.S. pursue closer trilateral cooperation to strengthen their anti-submarine warfare (ASW) capabilities.

The DPRK fields as many as 70 diesel-electric submarines. This fleet includes roughly 10 Yono-class “midget” submarines, 40 Sang-O class submarines, and 20 Romeo-class submarines.  These capabilities present a significant asymmetric threat to the U.S., Japan, and the ROK vessels, whether in peacetime or during a military contingency.  In 1996, the DPRK landed special operations forces on the ROK coastline. This botched reconnaissance operation resulted in 39 ROK casualties, including four civilian deaths.  In 2010, the DPRK went so far as to torpedo a ROK corvette, the ROKS Cheonan, as the U.S. and ROK conducted their annual Key Resolve/Foal Eagle joint exercise nearby.  The sinking of the Cheonan led to 102 ROKN casualties. 

More ominously still, the DPRK is developing around six new Sinpo-class ballistic missile submarines (SSBNs) while advancing its SLBM program.  The DPRK seems to have made significant progress on these systems with its first successful test in August of 2016. This presents still another threat to ROK, U.S., and Japanese interests – and opens another gap in their defense capabilities.  A mobile SSBN is more difficult to track and preempt than fixed launchers, complicating the ROK’s “Kill Chain,”  thus posing similar challenges for the U.S., Japanese, and South Korean Aegis missile-defense systems.  Even the new U.S.-ROK THAAD system may struggle to intercept SLBMs in certain circumstances.

Geographic obstacles and gaps in capabilities complicate the ability of local forces to counter these threats.  First, the geography of the seas surrounding the Korean Peninsula, particularly the West Sea, is inherently challenging for ASW. Second, ROK ASW capabilities may be inadequate to cope with the scale of these threats.  Although the ROKN has a cadre of professional, experienced ASW officers and is investing in new ASW capabilities, experts agree that significant gaps remain. The ROKN’s recent acquisition of new ASW helicopters is an important step toward remedying these gaps, but more extensive measures are necessary.  Third, despite the fact that any major maritime contingency around the Korean peninsula would likely involve ROK, U.S., and Japanese SDF assets, trilateral interoperability remains undeveloped.

Trilateral Cooperation: A Vital Step

To confront these challenges, the U.S., ROK, and Japan need to cooperate to upgrade their ASW capability around the Korean peninsula.  The recent General Security of Military Information Agreement (GSOMIA) – an accord strengthening intelligence and information-sharing between the three militaries – is an important step in the right direction, but deeper cooperation is needed.

First, the U.S. and its allies should set up regular defense exchanges at multiple levels – particularly seminars, symposia, and working groups.  In particular, the U.S.-ROKN ASW Cooperation Committee should be expanded to include the MSDF.  These exchanges should provide the allies the opportunity to share knowledge, expertise, and best practices while bolstering interoperability and working toward a common understanding of the operational environment and DPRK threat. 

Second, the allies should work toward the ability to develop contingency plans to respond to a range of scenarios involving ASW operations around the Korean Peninsula.  The three partners should discuss what roles each will play in a given contingency and how best they can aggregate their resources to secure their common interests.

Third, the allies should plan and hold joint ASW exercises to strengthen their interoperability and overall capability.  These exercises can also serve as an opportunity to practice trilateral contingency plans once they have been developed.    

ASW trilateralism offers clear benefits for the U.S. and its allies.  Most obviously, this coordination allows the three states to aggregate their capabilities, pool their resources, and share some of the burdens of confronting the DPRK submarine threat.  Beyond aggregation, this coordination is a “force multiplier” in that closer cooperation should also strengthen each contributors’ ASW capabilities – particularly the ROKN which can benefit from the expertise of the MSDF and USN.

This policy could also set the stage for closer cooperation between the two most important “spokes” in the U.S. system of bilateral alliances of Asia. Although the GSOMIA is an important first step, trilateral cooperation remains limited overall.  Cooperation in narrower activities like missile-defense and ASW where the ROK and Japan have clear overlapping interests and face common threats, however, can help build momentum and establish trust, facilitating broader and more difficult trilateral cooperation at the strategic level.

Just as importantly, trilateral ASW cooperation creates a powerful incentive for China to take more aggressive actions condemning DPRK’s provocative behavior. China sees efforts to deepen and broaden U.S. alliances in the region as threatening; its reactions to THAAD and GSOMIA highlight its suspicion toward stronger allied capabilities in Northeast Asia.  But if China refuses to cooperate in bringing the DPRK to heel over its nuclear program, the allies have little choice but to continue to strengthen their defensive capabilities.  The DPRK’s recent missile tests off Japan’s northwest coast have only reinforced this imperative for the U.S. and its allies, despite opposition from China. Upgrades to U.S. alliance capabilities will force China to make a choice: accept significantly stronger U.S. and allied capabilities in Northeast Asia, or break with Pyongyang.

A Difficult Path Forward

There are, of course, a number of hurdles to ASW trilateral cooperation.  The most significant is the current political turmoil in the ROK caused by President Park’s recent impeachment.  As Park struggles to defend herself against charges of corruption, her stand-in, acting president Hwang Kyo-ahn, will find it challenging to move forward with the type of ambitious cooperative measures that are necessary to defend the ROK.

Historical tensions compound these political difficulties. The failure of the ROK and Japan to successfully put the issue of comfort women to rest successfully with their recent accord has led to continued bitterness on both sides of the Sea of Japan.  In the maritime domain, the Takeshima/Dokdo island dispute continues to simmer with neither side willing to compromise their claims to sovereignty.

These obstacles have impeded ASW cooperation in the past.  In December 2016, the U.S. and Japan proposed trilateral ASW exercises as a means of building on the new GSOMIA but the ROK rejected the offer, claiming that the time was not ripe.  With the DPRK making major headway in its development of an SLBM, however, the ROK needs to reconsider this position.  Despite the political obstacles to closer cooperation with Japan, the ROK must push forward as soon as possible with trilateral exercises and exchanges – its security, and the stability of the region more broadly, are in the balance.

Without a strong leadership role on the part of the U.S., none of this will be possible.  The new U.S. administration must highlight its firm commitment to both of its allies if they are to buy into this politically challenging trilateral endeavor.  In particular, the U.S. administration should not allow its security partnerships to be undermined by disputes over trade deficits or host-nation support.  Secretary Mattis’ trip to the region to reassure Tokyo and Seoul of the U.S.’ enduring commitment to its allies and the successful meetings between President Trump and Prime Minister Abe represent steps in the right direction.  The U.S. needs to build on the momentum generated by these meetings to secure more extensive cooperation with its allies in pursuit of common defense objectives.

Erik French is a Ph.D. Candidate in Political Science at the Maxwell School of Citizenship and Public Affairs at Syracuse University, an Adjunct Instructor at American University’s School of International Service, and a junior fellow with the International Policy Scholars Consortium.  He is a Young Leader and former SPF Fellow with Pacific Forum CSIS. 

Jane Chung is a Young Leader at Pacific Forum CSIS. She received her Masters of Public Administration and International Relations from the Maxwell School of Citizenship and Public Affairs at Syracuse University.