The U.S.-Republic of Korea (ROK) alliance traditionally has focused on land rather than sea. Starting with the Korean War and throughout much of the Cold War, incursions south by the Democratic People’s Republic of Korea (DPRK) were the alliance’s greatest concern. Large-scale exercises to bolster interoperability and readiness concentrated, understandably, on land warfare, not naval operations.
Despite this legacy—and given current circumstances—the U.S.-ROK alliance has the potential to become a major maritime partnership that would have a substantial and mutually beneficial impact on allied interests at sea beyond the Korean littorals. The United States and the ROK should take steps to bolster this budding partnership, adopting an incremental approach to circumvent any Chinese opposition.
Shared Interests at Sea
The United States and the ROK share three major interests at sea in the Indo-Pacific. First, both have an interest in maintaining a favorable balance of power in the region, preferring that no state becomes a regional hegemon that could dominate other states. Such a hegemon would be a threat to the ROK’s political independence, sovereignty, and territorial integrity. An Asian hegemon would be secure enough at home to challenge the United States’ power and influence globally and could also threaten access to vital commerce in the Indo-Pacific, posing a major challenge for U.S. security and prosperity.1 As such, both allies are interested in ensuring that no potential competitor obtains a significant advantage in regional naval power.
Second, both the United States and the ROK are maritime trading states that depend on secure sea lines of communication (SLOC) for their economic well-being. The ROK imports almost all its energy, and these imports must travel through the Indian Ocean, South China Sea, and East China Sea.2 With an export-oriented economy, the ROK also depends on SLOCs to take its products to markets in Asia, North America, and Europe.3 The United States has a similar interest in secure SLOCs in the Indo-Pacific, which enable its exports to reach critical trading partners.
Third, both states value the core norms underlying the regional maritime order. These include respect for sovereignty and territorial integrity at sea and the peaceful resolution of maritime disputes.4 The United States and the ROK both espouse the basic tenets of the U.N. Convention on the Law of the Sea, including the right of innocent passage. In addition, both understand their interests in open commerce and the balance of power are strengthened and supported by these underlying principles.
Shifting Threats
The changing threat environment in the Indo-Pacific also creates a basis for a stronger U.S.-ROK maritime partnership. In particular, the two nations face diminishing land-based threats from the DPRK and expanding threats to their shared interests at sea.
While the DPRK’s nuclear program and bellicosity remain troubling, its Korean People’s Army (KPA) does not pose the same conventional threat it did during much of the Cold War. The KPA is still one of the largest standing armies in the world, but it fields antiquated Soviet weaponry, and it would have difficulty obtaining the critical supplies needed to sustain a ground war for any significant period of time.5 On top of this, fortified positions, rugged terrain, and an overwhelming advantage in allied airpower all reinforce the U.S.-ROK ability to deter or defeat a KPA incursion.6
In sharp contrast, the maritime threat environment looks increasingly severe. Rogue states such as Iran and nonstate actors such as pirates in the Gulf of Aden pose a risk to U.S.-ROK interests in a secure maritime commons. China is developing more capable antiaccess/area-denial capabilities, including submarines and antiship missiles, while at the same time increasing its ability to project power farther into the South China Sea and Indian Ocean.7 It already has deployed its first aircraft carrier and has several more on the way. In addition, China appears increasingly willing to leverage its naval might coercively to accomplish its goals in the region, particularly in the East China Sea, Taiwan Strait, and South China Sea. The ROK has experienced this Chinese assertiveness firsthand in disputes over its exclusive economic zone and the Ieodo rock in the Yellow Sea.
These developments undermine allied maritime interests. China’s rapid naval modernization has led to an ever-widening gap between China’s military power and those of its neighbors, eroding the regional balance of power. In addition, its naval power could be leveraged to threaten allied SLOCs and shipping and assert excessive territorial claims in the West Sea, East China Sea, and South China Sea, undermining the regional maritime order’s core principles.
ROK Naval Development
The potential for a U.S.-ROK maritime partnership is supported by the ROK’s expanding blue-water navy. Beginning in the 1990s, the end of the Cold War and the political transformation of the ROK triggered a rethinking of strategic priorities and a protracted national effort to modernize the ROK Navy—an effort that continues today.8
The ROK Navy has acquired a new generation of advanced destroyers geared toward blue-water missions.9 These include the KDX-III Sejong the Great–class, equipped with Aegis combat systems and a large complement of guided missiles. Three KDX-IIIs currently are in operation, with three more in production. The ROK Navy also is developing a new iteration of its Chungmugong Yi Sun-shin–class destroyers, the KDX-IIA, featuring new stealth technology, and has plans to develop a 5,000-ton arsenal ship capable of launching a large volume of cruise missiles against surface and land targets.
The ROK Navy is building larger and more capable attack submarines, including the KSS-III Dosan Ahn Changho class. The latest boats include air-independent propulsion systems to increase their undersea endurance. Three KSS-IIIs have been built, and six more are in development. In addition, the ROK Navy continues to consider nuclear propulsion for future KSS-IIIs, which would dramatically increase their blue-water potential.10
Just as significantly, the ROK Navy is developing its sea-based airpower. Its two LPX-I Dokdo-class landing helicopter platform amphibious assault ships can operate 10 helicopters or a small wing of short-takeoff/vertical landing (STOVL) aircraft, such as the F-35B. Even more notably, the ROK Navy’s Vision 2045 lays out plans for a light aircraft carrier (CVX) capable of operating a larger complement of STOVL aircraft.11
The ROK Navy has organized its first maritime task flotilla designed expressly for power projection beyond the Korean Peninsula.12 It has constructed a naval base on Jeju Island astride major SLOCs in the East China Sea. Together, these improvements will advance the ROK’s critical maritime interests and support a stronger alliance with the United States, one better suited to manage the emerging strategic competition in the Indo-Pacific region.
A Pathway Forward
The United States and the ROK already have begun to deepen their naval partnership. At the strategic level, their joint statements regularly proclaim the alliance to be a “linchpin” for regional security, drawing attention to the partnership’s broadening role and responsibilities.13 The alliance’s Future Defense Vision stresses the importance of “shared national security interests” beyond the Korean Peninsula.14 Most recently, President Joe Biden and President Jae-in Moon’s joint statement on 21 May 2021 emphasizes the allies’ commitment to “freedom of navigation and overflight in the South China Sea and beyond” and “preserving peace and stability in the Taiwan Strait.”15
At the operational level, the two nations have expanded their joint exercises and training at sea beyond the Korean littorals, participating in the multilateral Pacific Vanguard, Pacific Shield, and Rim of the Pacific exercises far from Korean shores. They cooperate side by side in the Combined Task Force 151 policing piracy in the Gulf of Aden and work with a coalition of other stakeholders through the enforcement coordination cell to interdict DPRK sanctions evasion efforts at sea.
Despite this important progress, the ROK’s concerns about antagonizing China pose a hurdle to further U.S.-ROK naval collaboration. Although the ROK shares U.S. concerns about China’s growing military power, it is wary of openly opposing Beijing. China is, after all, the ROK’s largest trading partner.16 China’s effort to veto the ROK’s installation of Terminal High Altitude Area Defense (THAAD) batteries for missile defense in its territory is a telling reminder of the ROK’s vulnerability to Chinese pressure.17
Nevertheless, the United States and the ROK can continue to strengthen their maritime partnership by adopting an incremental approach, taking gradual steps at the strategic and operational levels to bolster their naval cooperation.
At the strategic level, the allies should put a heavier focus on maritime cooperation in high-level consultations, including the Security Consultative Meeting, the ROK-U.S. Military Committee Meeting, and the Korea-U.S. Integrated Defense Dialogue. These dialogues provide leaders an opportunity to work toward a common vision of the U.S.-ROK role in maritime security, particularly in managing disputes in the Yellow, East China, and South China Seas. The two nations also would be well-served to sign a joint naval agreement, similar to the 2019 U.S.-U.K.-Japan trilateral naval agreement, affirming their commitment to a fortified naval partnership.18
At the same time, they should work to increase engagement with other key multilateral regional security dialogues. Specifically, the ROK should begin to participate alongside the United States in its existing trilateral consultations with Australia and Japan, including their annual Trilateral Strategic Dialogue. Similarly, the ROK should be brought into the Quadrilateral Dialogue encompassing the United States, Australia, Japan, and India. Through these dialogues, the U.S.-ROK partnership can bolster cooperation with other regional maritime stakeholders in pursuit of mutual interests.
The ROK and United States also can incrementally strengthen their maritime partnership at the operational level. U.S. presence in the ROK should shift to reflect changing circumstances in the Indo-Pacific. Right now, the ROK hosts roughly 19,500 U.S. Army soldiers but only 350 U.S. Navy sailors.19 This should change. A larger naval presence led by a higher-ranking U.S. naval commander would strengthen the relationship between the two navies. Permanently homeporting several U.S. surface combatants at the ROK naval base in Jeju could similarly improve the two nations’ naval ties.
The allies should conduct naval exercises farther from ROK shores, working alongside one another in blue-water environments along SLOCs in the Indian Ocean and South China Sea. These exercises could focus on an expanding range of activities, beginning with simple passing-and-maneuver exercises and growing to encompass underway replenishment, interdiction, antisubmarine warfare, air defense, and surface warfare. As the ROK begins to operate STOVL aircraft from the Dokdo class and CVX, joint exercises should encompass carrier aviation as well. This will strengthen the United States’ and the ROK’s ability to act jointly in the face of common threats at sea should the need arise. It also would send a powerful signal of their growing willingness to operate throughout the Indo-Pacific commons.
The United States must also encourage the ROK to participate in multilateral naval exercises.20 This should include the annual Malabar exercise alongside Australia, Japan, and India; La Perouse exercises with Australia, France, Japan, and India; and other similar training operations. These small steps would bolster the allies’ ability to work with like-minded regional maritime powers to secure their mutual interests in the Indo-Pacific.
The U.S.-ROK alliance faces mounting challenges to its shared interests at sea. With the ROK Navy poised to become a formidable blue-water force, the two nations should seek new opportunities for maritime cooperation. In the face of Chinese opposition, they will need to focus on slow but steady improvements to their naval collaboration if they are to realize the full potential of a maritime alliance. These steps will strengthen the U.S.-ROK partnership and ensure its enduring relevance in the face of intensifying great power competition.
1. Linde Desmaele and Luis Simon, “East Asia First, Europe Second: Picking Regions in U.S. Grand Strategy,” War on the Rocks, 7 August 2019.
2. U.S. Energy Information Administration, Country Analysis Executive Summary South Korea, October 2020, 1.
3. Terence Roehrig, “South Korea: The Challenges of a Maritime Nation,” Maritime Awareness Project, 23 December 2019, 1.
4. U.S. Department of Defense, Public Summary of Future Defense Vision of the Republic of Korea (ROK)-U.S. Alliance, 19 November 2019.
5. Kim Min-Seok, “The State of the North Korean Military,” in Korean Net Assessment: Politicized Security and Unchanging Strategic Realities, eds. Chung Min Lee and Kathryn Botto (Washington, DC: Carnegie Endowment for International Peace, 2020).
6. Michael O’Hanlon, “Stopping a North Korean Invasion: Why Defending South Korea Is Easier Than the Pentagon Thinks,” International Security 22, no. 4 (1998): 139–41.
7. U.S. Department of Defense, Military and Security Developments Involving the People’s Republic of China, 2020, 1 September 2020; LCDR James Turnwall, USNR, “The Navy Is Losing the Missile Arms Race,” U.S. Naval Institute Proceedings 145, no. 11 (November 2019); CAPT James E. Fanell, USN (Ret.), “Strike Groups with Chinese Characteristics,” U.S. Naval Institute Proceedings 146, no. 3 (March 2020).
8. Yoji Koda, “The Emerging Republic of Korea Navy—A Japanese Perspective,” Naval War College Review 63, no. 2 (Spring 2010): 8–11.
9. Robert Farley, “The South Korean Navy Has Big Plans Ahead,” The Diplomat, 23 August 2019.
10. Jihoon Yu and Erik French, “Should the United States Support a Republic of Korea Nuclear Submarine Program?” Naval War College Review 73, no. 1 (Winter 2020): 99–102.
11. LCDR Jihoon Yu, ROK Navy, and Erik French, “Why South Korea’s Aircraft Carrier Makes Sense,” The Diplomat, 27 March 2021.
12. Ian Bowers, The Modernisation of the Republic of Korea Navy: Seapower, Strategy, and Politics (London: Palgrave Macmillan, 2018), 101, 133.
13. U.S. White House, Joint Declaration in Commemoration of the 60th Anniversary of the Alliance between the Republic of Korea and the United States of America, 7 May 2013.
14. Department of Defense, Public Summary of Future Defense Vision.
15. U.S. White House, U.S.-ROK Leaders’ Joint Statement, 21 May 2021.
16. Uri Friedman, “How to Choose Between the U.S. and China? It’s Not That Easy,” The Atlantic, 26 July 2019.
17. Darren J. Lim, “Chinese Economic Coercion during the THAAD Dispute,” The Asan Forum, 8 December 2019.
18. Megan Eckstein, “CNO Gilday Signs Trilateral Cooperation Agreement with U.K., Japan Navy Heads,” USNI News, 20 November 2019.
19. Hyonhee Shin and Joyce Lee, “Factbox: U.S. and South Korea’s Security Arrangement, Cost of Troops,” Reuters, 7 March 2021.
20. For a similar idea, see: LCDR Andrew R. Poulin, USN, “The Global Maritime Coalition 2.0,” U.S. Naval Institute Proceedings 146, no. 3 (March 2020).
