Three Allies, One Undersea Turn: Korea, Japan and Australia Move Toward Nuclear Submarines

11/05/2026
By Robbin Laird

Three U.S. allies in the Indo-Pacific are now moving toward nuclear-powered submarines on different clocks and by different routes: Australia is already hosting the first American boat, South Korea has written a program and a budget line, and Japan has stopped ruling the option out. Together they signal a regional bet that long-endurance undersea power is the answer to distance, to China’s naval expansion and to North Korea’s own submarine ambitions.

South Korea: the conventional bridge to Jangbogo N

On 3 November, South Korea’s navy and the Defense Acquisition Program Administration launched the 3,600-ton submarine Seohui (SS-088) at Hanwha Ocean’s Okpo yard in Geoje, Newspim reports. Seohui is the second boat of Jangbogo-III Batch-II, contracted in 2021, laid down in 2024 and due for delivery in 2028. It is a conventional boat, and the launch was about the nuclear future anyway.

Batch-II is roughly six metres longer than Batch-I (about 89 metres against 83), and its vertical launch tubes grow from six to ten. Domestically produced lithium batteries replace lead-acid, and domestic content rises to 70 equipment items, 12 more than Batch-I. Those are the competencies a nuclear boat needs: indigenous design and construction, vertical launch, battery and power technology, and a domestic supplier base. The DAPA official who spoke at the launch, Lee Sang-woo, heads the agency’s nuclear-powered submarine program group.

The quiet signal is in the 2027 budget request. Newspim reports that ₩96.6 billion for the nuclear submarine is filed under the heading “Jangbogo-III Batch-III.” Batch-III was originally a conventional follow-on. A year ago, the day after the Korea–U.S. summit, the Navy Chief of Staff told the National Assembly that no Batch-III start date had been set. Filing nuclear money under a conventional batch name folds a politically sensitive program into an established acquisition line, industrial base and schedule. That is a reading of a budget classification, not an announced cancellation, and ₩96.6 billion is a first-year line against an estimated program cost of about ₩28.9 trillion.

On 26 May the government named the program Jangbogo N. Its stated principles are low-enriched uranium fuel below 20 per cent, domestic development and construction, indigenous hull and propulsion, whole-life-cycle management, a first launch in the mid-2030s and service entry in the late 2030s. At least three boats are under discussion, with conventional armament. USNI News reports the stated mission is to counter North Korea’s submarine-based missile threat, including by shadowing its boats as they leave port.

What is unresolved is fuel and law. Seoul and Washington opened talks in Seoul on 2–3 June on the submarine plan and on enrichment and reprocessing rights, and the Korea Herald notes that under the 123 Agreement enrichment requires U.S. approval that has never been granted, and the agreement bars U.S.-supplied nuclear material from military use. The Korea Times reports three legal pathways under discussion: a full revision, a partial amendment, or new enforcement decrees. There is also a loose end on location. USNI reports President Trump said the boats would be built at Hanwha’s Philly Shipyard, while Seoul’s Defense Ministry document says they will be built entirely in South Korea.

Japan: from taboo to “not ruling anything out”

Japan has the furthest to travel and the heaviest legal baggage, and the debate has moved quickly. On 11 September Defense Minister Shinjiro Koizumi said Tokyo will not rule out nuclear-powered submarines while it revises its three key security documents, Naval News reports. He stressed that no decision has been made. He also listed the costs: SSNs are noisier, cost more, need larger hulls and require specialist expertise, against the advantages of long submerged endurance and speed several times that of a conventional boat.

The path to that statement is short. A Ministry of Defense expert panel recommended studying next-generation propulsion in September 2025. After Washington approved the Korean program, Koizumi pushed the debate in November 2025, and a former defense minister said the next-generation boat would eventually need nuclear propulsion. By June 2026 the Japan Innovation Party, the junior coalition partner, was calling for swift introduction, a deployment plan and a significant budget increase. Its proposals went further than the senior Liberal Democratic Party, which speaks only of “next-generation propulsion.” The revised documents are due by the end of 2026.

Japan’s present fleet shows both the strength and the limit of the conventional path. According to Defence Security Asia, Shogei, the seventh Taigei-class boat, has just launched at Kobe. It is lithium-battery powered, still has to snorkel to recharge, and has no vertical launch system. A separate larger design with vertical launch is in study, and Mitsubishi Heavy Industries received a design research contract in July 2026 that runs through fiscal 2029. Nothing has been approved: no reactor design, program or schedule.

The hurdles are not only technical. The Atomic Energy Basic Act limits nuclear energy to peaceful purposes, and a nuclear boat would need a crew of about 100 against about 70 for a Taigei, plus reactor support infrastructure. Opposition is organized. A Xinhua report from Tokyo on 21 October, which quotes only critics, describes seminars and a Diet protest against the idea, and Beijing’s framing is easy to anticipate. Whatever Japan decides, it will decide in public, and slowly.

Australia: from plan to boats in the water

Australia is the one of the three that has crossed the line, and it did so with a partner who already owns the industrial base. On 26–27 October the AUKUS partners named USS Colorado (SSN 788) as the first Virginia-class boat for Submarine Rotational Force-West, with assignment beginning in late 2027, The Defense Post reports. The force will operate from HMAS Stirling in Western Australia and is projected to host up to four American submarines and one British boat on rotation.

Colorado arrived at Stirling on 27 October for a planned maintenance period before deployment. More than 30 Australian civilian technicians from ASC are working on a Virginia-class submarine in Western Australia for the first time, the third such maintenance period in 12 months. Rear Adm. David Mann of the Australian Submarine Agency called it “the ultimate integration of a UK, US, and Australian workforce.” The joint statement ties the rotation to Australia’s readiness to operate and sustain a sovereign, conventionally armed, nuclear-powered fleet and says activities will be consistent with obligations under the Non-Proliferation Treaty.

The acquisition itself was simplified at the end of May. At the AUKUS defense ministers’ meeting in Singapore, the partners announced that the United States will sell Australia three in-service Virginia-class boats, replacing the earlier plan of one new Block VII and two in-service Block IV boats, USNI News reports. Defence Minister Richard Marles said the change eases the burden of running four classes: Collins, used Virginias, new Virginias and SSN-AUKUS. Sales are still slated for the 2030s and the British-Australian SSN-AUKUS for the 2040s.

The constraint is American shipbuilding, not Australian ambition. Navy officials say the industrial base must reach 2.33 attack boats a year, in addition to one Columbia-class boat a year, to support the sale, and it builds about 1.3 now. The Chief of Naval Operations told Congress on 12 May that he expects two a year in 2032.

What the three share, and what is still open

The three programs are at different stages, but they face the same underlying argument. Distance in the Indo-Pacific rewards submerged endurance, and a boat that can stay on station for months changes what a fleet can hold at risk. For a kill web, the nuclear boat is a long-endurance node that can shoot, sense and carry other nodes. Korea’s ten vertical launch tubes and Japan’s interest in a vertical-launch design point the same way, toward boats that contribute strike and targeting capacity to a wider network. AUKUS Pillar II adds the other side of the picture: USNI reports that its first program is an uncrewed undersea vehicle effort with deliveries from 2027. The manned nuclear hull and the uncrewed mesh are likely to be designed together, not in sequence.

The harder lesson is in the sustainment. Australia’s early step was not a boat but 30 technicians doing maintenance at Stirling. Korea’s early step was a battery, a launch tube and a budget heading. Japan’s is a legal review. Each of the three has discovered that the reactor is the smallest part of the problem, and that fuel, industrial base, crews, law and allied trust determine whether a program produces boats.

  Australia South Korea Japan
Status U.S. rotation from late 2027; three in-service Virginias to be sold Jangbogo N plan published 26 May; first nuclear budget line in 2027 request No decision; options open in security document revision due by end 2026
Timeline Sales in the 2030s; SSN-AUKUS in the 2040s First launch mid-2030s; service late 2030s None approved
Main open question U.S. build rate: about 1.3 attack boats a year against 2.33 needed Fuel: U.S. approval for enrichment and a 123 Agreement pathway; build location Atomic Energy Basic Act, a crew of about 100, reactor infrastructure

There is also a question the three capitals do not control.

An unnamed U.S. Navy official speaking in Hawaii reportedly said in September that Japan considering SSNs made sense given its nuclear power plants and technology, while Korea needed a “valid reason” and should not pursue them as a status symbol, according to the Naval News account cited above.

Washington is therefore not a neutral supplier.

It is the fuel source, the shipbuilder, the treaty partner and, in effect, the licensing authority for what its allies can do, and the three allies will watch one another’s treatment closely.

Sources