The Optimum Pathway for Building Nuclear Submarines with South Korea and Japan

By Brent D. Sadler

Introduction

Driving a wave of success throughout his Asia tour, President Donald Trump triumphantly introduced the U.S. could be working with South Korea to construct nuclear submarines.1 To these acquainted with the AUKUS (Australia-U.Ok.-U.S.) deal, this may increasingly appear a repeat of that effort to construct nuclear submarines with Australia. By all accounts, this isn’t what’s at hand.

South Korea’s rising funding in American shipbuilding might foster the event of ships able to utilizing subsequent technology small modular nuclear reactors (SMNR), to incorporate their use on modified South Korean submarines applicable to their operational wants. This likewise has applicability to Japan, who ought to be included ought to the trouble proceed.

Given the distinctive naval wants of South Korea and Japan, their many years of expertise in constructing typical submarines, and the U.S. want for allies in reviving its maritime trade – this deal may very well be very opportune. That stated, it is not going to be AUKUS and to succeed it should additionally contribute to a revival of America’s shipbuilding to finest serve America’s nationwide pursuits. 

South Korea’s Nationwide Safety Scenario

South Korea’s capital, Seoul, is inside vary of a whole lot of North Korean artillery items. For them hazard is at all times close to, and has centered their navy to the risk ever because the armistice paused the Korean Conflict.2 Including to the hazards, the North has lately accelerated growth of its personal nuclear-armed submarine-launched ballistic missile – the Pukguksong collection that started testing in 2015 and now has six iterations.3 Given this at-sea nuclear risk, as within the Chilly Conflict, there will probably be a necessity of finding and conserving monitor of North Korean submarines with nuclear-armed SLBMs, just like the SSB 841 Hero Kim Kun Okay launched in September 2023.4

Past the North Korean risk, China has additionally encroached into its waters and strong-armed the South. Most notably, the Chinese language Communist Occasion was the hand behind political interference and public agitation in 2017 over the position of the THAAD missile protection system.5 Protecting its economic system freed from coercion would require a Navy capable of hold the Individuals’s Liberation Military Navy (PLAN) in verify within the East China Sea and Yellow Sea. Ought to struggle get away in Asia over the destiny of Taiwan, essential delivery routes via the South China Sea and probably throughout the North Pacific will should be guarded. 

Not like the Australian strategic challenges that drive them to pursue a nuclear submarine within the AUKUS initiative, South Korea’s maritime threats are nearer to house. This operational state of affairs prioritizes stealth and on-station endurance with the power to conduct high-speed sprints with no need to come back close to to the floor to recharge submarine batteries. These operational necessities inform South Korea’s submarine program, at the moment led by manufacturing of its 3,600 ton KSS-III Batch-2 submarine with 10 vertical launch cells and torpedo tubes constructed by shipbuilder Hanwha.6 SMNRs supply a method to improve the lethality on a probably modified South Korean submarine like a future batch of the KSS-III.

A Transient Historical past of SMNRs Backfitted on Standard Submarines

Twice within the current previous have navies tried to increase the undersea endurance of current typical submarines with small modular nuclear reactors. The primary was within the mid-Nineteen Eighties, when the Soviet Navy put in a 600kWh VAU-6 600 nuclear energy plant on a challenge 651 (Juliett-class) diesel submarine and tremendously prolonged its vary.7 The implications of this growth have been by no means felt within the West, because the Chilly Conflict was coming to a speedy finish by the point this was accomplished.

The thought of tremendously growing the tactical capabilities of current conventionally-powered submarines has surfaced once more. For the previous a number of years, consultants trying over satellite tv for pc photos of China’s sole naval nuclear shipyard at Huludao have seen the growth of manufacturing traces and what appeared as parts of a brand new class of nuclear-powered warship. The reply could be clear in September 2024 following months of hypothesis {that a} new bigger Yuan-class typical submarine was being readied for sea with a brand new kind of propulsion.8 That month, reviews of its pier aspect sinking drew a subsequent U.S. Division of Conflict response that confirmed it was a variant being fitted out with an auxiliary nuclear energy plant. And so the Soviet thought was reborn with Chinese language traits.

Given China’s massive and fashionable conventionally powered submarine fleet, its use of SMNRs to enhance air impartial propulsion would have extreme ramifications for the U.S. and its allies. Already pretty stealthy, the most recent Yuan-class Chinese language submarine would see its endurance tremendously prolonged and survivability improved with the power to dash at excessive speeds to evade hostile contacts with out having to come back to the floor to recharge its batteries quickly afterwards. Furthermore, the restricted nuclear building capability at Huludao may very well be augmented by quite a few typical submarine shipyards, with SMNRs being produced and backfitted on Yuan-class submarines in shipyards like Wuchang and Jiangnan.

Shared Allied Curiosity in SMNRs

As information broke of President Trump’s announcement on constructing nuclear submarines with South Korea, Japan additionally acquired .9 Japan isn’t any stranger to maritime nuclear propulsion with its personal Mutsu launched in 1969 and retired in 1992.10 This ship was a flawed try at exploring the business potential of nuclear energy, with unacceptable radiation leakage dooming the ship. Just lately, there have been calls by Japanese politicians to pursue growing a nuclear submarine – a name first triggered by the AUKUS initiative in 2021 and now with a possible U.S.-South Korean challenge.

Like South Korea, Japan too has a sturdy, profitable, and longstanding typical submarine program. The newest addition to the Japanese Maritime Self Protection Forces (JMSDF) is the three,000 ton Taigei-class.11 Nevertheless, Japan’s operational wants are extra prolonged than South Korea’s, given its expansive archipelago that stretches deep into the Pacific Ocean and demanding delivery lanes threatened by Russia, China, and North Korea. This risk is partially why Japan started a navy modernization in the course of the later Chilly Conflict to guard its delivery lanes 1,000 miles from Japan – a mission that lives on at the moment. As such, the added endurance and survivability provided by SMNRs as an augmented energy supply for current typical submarines could be welcome.

Moreover, each Japan and South Korea are at the moment the one viable rivals to China’s shipbuilding colossus. As such, each need to put money into the U.S. as a way of increasing market share, which may very well be amplified by harnessing the potential of SMNRs to cleanly energy the subsequent technology of economic ships and revolutionize the maritime trade. Nevertheless, solely the U.S. has the expertise (because of its naval nuclear program) and capability (primarily based on current nuclear analysis and growth) to deliver this new nuclear expertise shortly to market with confidence.

Current developments have the hallmarks of a possible consortium of buyers forming to deliver SMNRs to sea and shortly. Already two South Korean shipbuilders have invested within the U.S. and Japan has signaled investments are coming. What particularly stands out is the investments since December 2024 in Philadelphia Shipyard by South Korean shipbuilder Hanwha. The proverbial canary within the coal mine is how properly Hanwha will have the ability to flip a revenue in the long run when taking orders for business ships at its new American shipyard.

Newer to the scene is Hyundai, one other South Korean shipbuilder, who has joined right into a partnership with American naval ship and submarine builder Huntington Ingalls Industries (HII).12 The scope of this new partnership is comparatively undefined as of November 2025, however indicators an intent to deeply combine into home American naval shipbuilding. Essentially the most specific expression of this can be a dedication of $150 billion by the South Korean authorities to again funding in American shipbuilding.13 Alternatively, Japan has solely not too long ago signaled its intent to maneuver into the American market, with $4 billion of presidency backing to $2.5 billion of personal funding.14 Focusing a few of this overseas funding in what may very well be a market-setting expertise can leverage the shipbuilding capacities and experience of allies, whereas mitigating the dangers in getting SMNRs to sea.

Proliferation and Compromised Provide Chain Issues

Within the case of each Japan and South Korea, there are grounds for concern concerning the potential for compromised maritime industrial provide chains and knowledge safety. Much less of a priority is the specter of proliferation of weapons-grade nuclear materials within the SMNRs underneath growth. This is because of using decrease enriched nuclear gasoline (roughly 5% in comparison with weapons grade above 90%) and the gasoline assemblies that complicate the separation and refinement of the gasoline to weapons grade.

Nonetheless, recollections of Brazil’s previous makes an attempt to develop a nuclear submarine as pretext for a nuclear weapons program are informative and cautionary.15 Placing a verify on such potentialities are counter-proliferation protocols enshrined within the so-called “123 settlement” named for the part 123 of the 1954 Atomic Power Act. These agreements are conditional by the U.S. previous to coming into into any agreed switch of nuclear expertise or supplies. Each Japan and South Korea have lively 123 Agreements.16

Concerning maritime provide chains, nonetheless, each Japan and South Korea conduct important shipbuilding associated exercise in China.17 That is primarily within the prefabrication of sections or modules and provide of parts like pumps or solenoids which might be then assembled outdoors China. Ought to both nation enter into a brand new SMNR developmental challenge and related shipbuilding endeavor with the U.S., publicity to related Chinese language provide chains should be addressed, particularly because it pertains to navy use in South Korean and Japanese submarines.

Lastly, tight data safety, similar to carried out with Naval Nuclear Propulsion Data (NNPI) addressed for AUKUS, will probably be a necessity. A complicating issue for allies would be the dual-use applicability of SMNRs and the way to make sure related excessive data safety for each navy and business packages. Fortunately, the U.S. has present information-sharing agreements with each Japan and South Korea that features industrial safety. In 2025, memorandums of understanding signed with each South Korea and Japan clarify an intent to bolster provide chains because the three nations progress and work collectively in reviving America’s maritime trade.18 Nevertheless, statements of intent usually are not sufficient to make sure the delicate next-generation nuclear energy expertise behind SMNRs stays an American comparative benefit.

The Optimum Pathway for American Maritime SMNR

Growing SMNRs after which placing them to sea on business and backfitted allied typical submarines will probably be a multifaceted job. First, the expertise must be perfected in a method that makes it suitable to be used in business delivery and scaled to be used in its place energy supply for at the moment’s typical submarines inbuilt Japan and South Korea. Second, belief in sharing delicate nuclear applied sciences for SMNR will probably be wanted, to incorporate their protected operation and upkeep. Third, an industrial plan will should be applied for constructing SMNRs that may be put in on business ships and on allied conventionally powered submarines. To protect American funding in growing subsequent technology SMNR and foster an American comparative benefit within the world maritime market area, building and set up ought to be initially confined to happen at U.S. shipyards. A lot of this may be completed taking an analogous method used for the AUKUS optimum pathway and as advocated in an earlier Heritage Basis report.19

Nearly two years after its September 2021 announcement, the Australian authorities, in live performance with U.Ok. and the U.S., introduced the “optimum pathway” to ship a home nuclear submarine functionality.20 This plan addresses growing home nuclear industrial competencies, coaching a cadre of nuclear-certified shipyard staff to maintain this nuclear fleet, and start the nuclear coaching of the crew of those future boats. Not like AUKUS, growth of abroad SMNR building wouldn’t be a purpose. Nonetheless, bringing a SMNR ahead with allies like South Korea and Japan would require a equally multifaceted method to make sure it’s viable and protected.

Suggestions

The U.S. and its allies ought to kind a private-public consortium to tell and oversee growth of a naval SMNR. There are a number of designs all progressing to working prototypes with preliminary criticality (first time nuclear fission) assessments earlier than the top of the last decade.21 This consortium could be essential in accelerating the testing and maturity of viable designs at present being deliberate on the federal nuclear take a look at labs in Idaho (i.e. INL). Given the business and potential navy use, the trouble ought to be led by U.S. Division of Power with technical help from Naval Reactors (design), Coast Guard (regulatory), and Maritime Administration (business use).

Placing an operational SMNR on a business ship or submarine is probably going not less than seven years away. Ready till that point to develop the demand for business delivery would assure its failure or worse, cede dominance of this functionality to hostile competitor China. As such, orders for brand new business ships (i.e. extremely massive container ships, LNG carriers, and so forth.) at the moment ought to be of designs which might be forward-compatible for set up of SMNRs.22 This might additionally assure these ships meet stringent Worldwide Maritime Group (IMO) carbon necessities whereas eradicating uncertainty that has delayed ship orders over which inexperienced power will probably be embraced by the market. Because the second and third largest shipbuilders, Japan and South Korea are finest positioned to make sure uptake of this new expertise. Furthermore, data safety amongst members of this consortium will probably be paramount, particularly as variants of the SMNR are put in on allied submarines. For AUKUS, this was an early achievement given the bedrock of the 5 Eyes intelligence sharing program.23 A equally structured method, however narrowly centered on SMNR use, could be warranted with allies Japan and South Korea.

As we speak there may be one U.S. shipyard owned by a South Korean shipbuilder. Philadelphia Shipyard, owned by Hanwha since December 2024, is a pure option to base this new endeavor and future SMNR installations. Already Hanwha is continuous the U.S. Maritime Administration’s (MARAD) third of 5 Nationwide Safety Multi-mission Vessel (NSMV) and making a $5 billion capital funding to improve the shipyard for orders of 10 new medium-range tankers and bulk carriers.24 Doing nuclear shipyard work right here would require added investments to draw future SMNR builders to find fabrication and set up amenities close by. Within the meantime, future upgrades ought to be carried out with an eye fixed to nuclear certification of the yard.

This shipyard shouldn’t be the one place the place such a business nuclear maritime set up will happen. Given the nationwide safety features of backfitting SMNRs on submarines, shipyards with historical past in naval shipbuilding take advantage of sense. On this case, the experience of HII and its budding partnership with Hyundai makes a pure match for backfitting operations of SMNRs. Warning is warranted on this case, because the U.S. submarine industrial base is tardy in rising its capability to satisfy U.S. orders for nuclear submarines.25

As such, HII and Hyundai, to incorporate Japanese submarine builders Kawasaki and Mitsubishi Heavy Industries, with American submarine shipbuilders HII and Electrical Boat, ought to look to arrange amenities favorable to shipyards not concerned in constructing American or AUKUS nuclear submarines. A logical selection is the previous naval nuclear shipyard at Mare Island, which has dry docks, warehouses, and pier area able to be upgraded to the aim. Furthermore, there may be ongoing Navy and Coast Guard upkeep being carried out on cutters and naval logistic ships, offering ample workload to justify the funding till SMNRs change into operational.

Designing, constructing, and putting in SMNRs on business ships and allied submarines is one factor, working them is one other. For AUKUS, this was addressed by embedding Australian sailors on U.S. and U.Ok. nuclear submarines and sending Australian shipyard staff to American shipyards to study the nuclear trades. It’s too early to know if this may succeed, however the purpose is to create the institutional tradition and experience to securely preserve and safely function nuclear-powered ships. Not like AUKUS, this new SMNR endeavor can have a business facet which can imply the U.S. Maritime Administration and its Service provider Marine Academy at Kings Level might want to resurrect its defunct nuclear coaching program. This program was begun to crew and conduct related shipyard nuclear work for the primary and solely U.S. nuclear powered business ship in 1964 – the Savannah, subsequently retired in 1972. The U.S. Coast Guard, the lead company for regulating maritime credentials within the U.S., too should revisit its certification packages to incorporate requirements for crew and shipyard staff on SMNR-powered business ships. On condition that allies will probably be concerned, related packages should be opened for his or her coaching and certification. 

Preliminary Steps

There will probably be plenty of work forward ought to the President’s phrases show prophetic, and a brand new nationwide endeavor is launched with allies to construct nuclear-powered business ships and backfit allied typical submarines. When AUKUS was introduced an 18-month evaluation and planning section was begun earlier than precise work was undertaken. An identical planning effort will probably be essential, although needn’t be so long as 18 months. Given this, a possible optimum pathway for SMNRs ought to take the next steps.

Set up a White Home-Led Planning Cell. The President of america ought to formally invite each Japan and South Korea to ship delegates to a planning cell to formulate a pathway to growing and working SMNRs for business delivery and backfitting their conventionally powered submarines. The first purpose of this group is to provide an agreed regulatory framework, credentialing program, and industrial plan with related funding technique. This in whole would characterize the optimum pathway for this endeavor.

Reestablish Civilian Nuclear Coaching and Credentialing Applications. The Secretary of Transportation ought to direct the Maritime Administrator to re-establish the nuclear program on the Service provider Marine Academy and search funding from Congress. This ought to be completed inside two years to make sure adequately credentialed crew and shipyard staff prepared when the primary SMNR put in and operated by early 2030s. Moreover, the Maritime Administrator should additional direct these packages be open to collaborating allies, workers, and college students to make sure a coherency amongst contributors and help in quickly standing up an SMNR-powered business fleet. Lastly, the U.S. Coast Guard should conduct a evaluate and as wanted replace to its credentialing and regulatory requirements applicable for working SMNRs at sea and related shipyards and port operations.

Create an SMNR Data Sharing Framework. The U.S. Chief of Naval Operations ought to direct the event and approval of a devoted data sharing classification and dealing with commonplace that may be agreed to by all participant nations. This might be comparable however distinct from Naval Nuclear Propulsion Data that Australia was allowed to achieve entry to as a part of AUKUS. The purpose is to stop unauthorized entry to delicate design and operational particulars concerning SMNR in each business and navy makes use of.

Designate and Certify American Shipyards for SMNR Work. The Secretary of Power ought to search and act on the advice of Naval Reactors and the Maritime Administration to designate shipyards for work on maritime SMNRs. Initially two shipyards ought to be named – one specializing in the business makes use of and a second appropriate for naval set up on typical submarines.

Set up SMNR Help Services in Participant Nations. The Secretary of State, with the recommendation of Submarine Forces Pacific and the Maritime Administrator, ought to replace current nuclear agreements and set up help amenities abroad. Initially, the one contributors to think about ought to be main shipbuilders and treaty allies South Korea and Japan. As such, business and navy amenities ought to be established in each international locations to help future SMNR operations. In the interim, all main refueling and upkeep ought to be performed within the U.S. Importantly, each Japan and South Korea (re-negotiated in January 2025) have already got “123 Agreements” with the U.S. for peaceable nuclear cooperation.

Conclusion

President Trump’s feedback might have preempted and even accelerated what has been a slowly growing effort – joint growth and operation of at-sea SMNRs. Accomplished proper, superior SMNR expertise will supply an avenue to develop a brand new American maritime industrial comparative benefit whereas quickly making allied typical submarines many occasions extra deadly towards rivals.

Captain Brent Sadler (Ret.) joined the Heritage Basis as a Senior Analysis Fellow in 2020 after a 26-year naval profession in nuclear submarines and as a overseas space officer. He has in depth operational expertise within the Western Pacific, having served at Seventh Fleet, Indo-Pacific Command, as Protection Attache in Malaysia, and as an Olmsted Scholar in Tokyo, Japan.

References

[1] Paul McLeary and Phelim Kine, “Trump Will Arm South Korea with a Nuclear Submarine,” POLITICO, October 29, 2025, (accessed November 9, 2025).

[2] Terence Roehrig, “South Korea: The Challenges of a Maritime Nation,” NBR, December 23, 2019, (accessed November 9, 2025).

[3] Sam-man Chong, “The Implications of North Korean SLBM for KSS-III Submarines,” Korea Institute for Maritime Technique, January 27, 2024, pg. 2-3, (accessed November 9, 2025).

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[7] “VAU-6 Auxiliary Nuclear Energy Plant (ANPP) Dollezhal eggs – Submarines,” International Safety, (accessed November 9, 2025).

[8] Brent Sadler, “China’s Nice Submarine Sinking: What We Know and Why It Issues,” Nationwide Safety Journal, October 9, 2024, (accessed November 9, 2025).

[9] “Japan Eyes Nuclear Subs After U.S. Provides OK to S. Korea,” Asahi Shimbun, November 7, 2025, (accessed November 9, 2025).

[10] Kaoru Ohno, “Nuclear Powered Ship Mutsu Designated as Particular ‘Ship Hertiage’,” Japan Atomic Industrial Discussion board Inc., (accessed November 9, 2025).

[11] Kosuke Takahashi, “Japan Launches Sixth Taigei-class Submarine,” Naval Information, October 14, 2025, (accessed November 9, 2025).

[12] “Huntington Ingalls, HD Hyundai Signal MOA to Increase US-Korea Shipbuilding Cooperation,” WorkBoat, October 27, 2025, (accessed November 9, 2025).

[13] Chris Panella, “White Home says South Korean shipbuilding giants are going to pour billions into reviving America’s shipbuilding trade,” Enterprise Insider, October 29, 2025, (accessed November 9, 2025).

[14] “Report: Japan and U.S. to Signal Memorandum on Shipbuilding Cooperation,” The Maritime Government, October 26, 2025, (accessed November 9, 2025).

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[16] “123 Agreements for Peaceable Cooperation,” U.S. Division of Power, July 11, 2025, (accessed November 11, 2025).

[17] Kawasaki Heavy Industries (KHI) has important operations in China throughout numerous enterprise segments, together with shipbuilding, robotics, hydraulic gear, and environmental techniques, primarily via joint ventures and native subsidiaries: (accessed November 11, 2025).

Mitsubishi Heavy Industries (MHI) doesn’t have wholly-owned shipyards constructing full vessels in China, however it has a number of joint ventures, licensing agreements, and repair operations within the nation associated to marine equipment, engines, and engineering companies: (accessed November 11, 2025).

Hanwha Shipbuilding has operations in China, particularly a shipyard in Shandong province that builds ship parts for remaining meeting in South Korea. These parts are essential to the corporate’s manufacturing and provide chain: (accessed November 11, 2025).

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[19] Brent D. Sadler, “AUKUS: U.S. Navy Nuclear-Powered Ahead Presence Key to Australian Nuclear Submarine and China Deterrence,” The Heritage Basis, October 27, 2021, pg. 7-9,

[20] “Pathway to Australia’s Nuclear-Powered Submarine Functionality,” Australian Submarine Company, March 14, 2023, (accessed November 9, 2025).

[21] “Superior Small Modular Reactors (SMRs), U.S. Division of Power, (accessed November 9, 2025).

[22] Brent D. Sadler and Peter St. Onge, “Regaining U.S. Maritime Energy Requires a Revolution in Transport,” The Heritage Basis, Might 15, 2023, pg. 18-20, (accessed November 9, 2025).

[23] Adam Broinowski, “AUKUS Pillar 2,” Parliament of Australia, August 15, 2024, (accessed November 9, 2025).

[24] “Hanwha Publicizes $5 Billion Philly shipyard Funding as A part of South Korea’s Dedication to US Shipbuilding Progress,” Hanwha, August 25, 2025, (accessed November 9, 2025).

[25] “U.S. Navy Shipbuilding Is Persistently Over Price range and Delayed Regardless of Billions Invested in Trade,” GAO, April 8, 2025, (accessed November 9, 2025).

Featured Picture: The JMSDF submarine Taigei (SS-513) (JMSDF picture).