Nuclear subs provide South Korea a security hedge, potential for nuclear weapons

SEOUL, South Korea — The nuclear submarines President Trump green-lighted in his meeting with Lee Jae-myung last month may help the South Korean president reassure a public wary of an upcoming shakeup over control of South Korea’s troops — and move Seoul closer to developing nuclear weapons.

Mr. Lee, leading a liberal party that has customarily sought increased defense autonomy, has vowed to regain operational control of South Korean troops in wartime — or “OPCON Transfer” — from the U.S. by the end of his term in 2030.

With Mr. Trump demanding more of allies, that looks on point. But the move has been slow-walked since the early 2000s as it could have effects across the alliance.

Though the subs would be nuclear-propelled, not nuclear-armed, the deal is huge. Washington has shared related technologies with only one ally, the U.K., while Australia is also set to receive them per the 2021 AUKUS agreement.

The only other countries operating nuclear boats are China, France, India and Russia.

The agreement has multiple moving parts — technical, strategic and political. However, no subs — Seoul would need a minimum of three — are likely to launch before the late 2030s.

The great unspoken possibility is nuclear fuel enrichment, which would inch Korea toward a capability widely discussed, but never officially, among Seoul pundits: An atomic weapon.

Operational issues

Nuclear subs offer limitless range, but the South Korean Navy’s core mission is close-in: deterring North Korea. Still, its horizons have expanded.

A retired U.S. arms salesman recalled a Korean request in the late 1990s for long-distance, encrypted communications to talk to subs in the Malacca Strait.

The strategic maritime trade passage lies 2,500 nautical miles from the Korean peninsula.

Seoul has sought nuclear boats for “at least two decades,” said Yu Ji-hoon, a retired South Korean navy commander. The acquisition gained “urgency after 2016, when North Korea accelerated its development of submarine-launched ballistic missiles.”

Attack submarines provide one counter. Nuclear boats can remain submerged, on shadowing or ambush missions, longer than diesel-electric subs, which Seoul has been manufacturing and operating for 34 years.

“The primary and immediate rationale is very clear: Countering the North Korean SLBM threat,” said Mr. Yu, a research fellow at the Korea Institute of Defense Analysis. “However, Korea’s maritime interests extend well beyond its immediate waters.”

An export powerhouse and net energy importer, Korea relies on open sea lanes. In 2011, it conducted a commando strike on Somali pirates. Today, it joins multinational exercises as far flung as Australia.

Both dynamics require blue-water reach.

During the Moon Jae-in administration of 2017-2022, the possibility of adding nuclear propulsion to existing subs “entered policy-level review,” Mr. Yu said.

However, the first Trump administration rejected requests for the technology, said a U.S. source familiar with the discussions.

Asked why Mr. Trump shifted his stance, the source conjectured: “Maybe $350 billion” — the amount Seoul has pledged to invest in the U.S.

Power politics and public psychology

The same source warned, however, that if Seoul truly seeks defense autonomy, there are higher priorities than super-expensive nuclear subs.

Those priorities include expanded intelligence, reconnaissance and surveillance assets, and massively increased stockpiles of smart munitions — ground and air-launched missiles, artillery shells and drones, he said.

A foreign naval officer, speaking off the record, sniffed at Korean desires for “big, shiny toys.”

That critique points to the primacy of domestic political issues.

OPCON Transfer was initiated by the liberal Roh Moo-hyun administration (2003-2008). It is expected to collapse the current — and potent — joint war-fighting staff structure, Combined Forces Command, led by a U.S. general, and otherwise affect the alliance.

Successive conservative administrations applied the brakes on the move. Mr. Lee, who took office in June, hit the accelerator.

“The right traditionally don’t want to do anything to weaken U.S. commitment,” said Mike Breen, Seoul-based author of “The New Koreans.” “The left focuses on Korea’s embarrassing level of dependence.”

Korean liberals’ demands for upgraded military punch blow a hole in accusations sometimes made by U.S. conservatives: “Lee is weak on security.”

His florid posture may quiet nerves at home.

Nuclear subs could “placate retired admirals and generals, a big lobby group,” said Daniel Pinkston, an international relations expert at Seoul’s Ewha University. “Procure sophisticated naval vessels and the admirals are on board.”

Yang Uk, a defense analyst at Seoul’s Asan Institute, said the navy’s win from Mr. Trump stems from Mr. Lee’s distaste for the army: Army commandos undertook the botched auto-coup by conservative former President Yoon Suk Yeol in December.

Mr. Yang suggested an under-informed public is an issue. “We don’t have nuclear weapons, but a nuclear-powered sub looks like a nuclear weapon,” he said.

U.S. Navy Chief of Operations Adm. Daryl Caudle voiced during a visit to South Korea his “natural expectation” that the subs would be used to deter China.

Mr. Lee mentioned that factor to Mr. Trump during their October meeting.

While admitting that “blue water missions” are not the Korean navy’s “main driver,” Mr. Yu said nuclear subs — he anticipates a flotilla of at last three boats — would “expand Korea’s capacity to operate alongside U.S. naval forces across a wider operational area” in terms of “joint patrols, combined [anti-submarine warfare] operations and coalition responses to regional contingencies.”

Mr. Yang, who is dubious about the vessels’ utility to deter North Korea, sees one upside.

“This could be a blessing in disguise,” he said. “It might give us the courage to stand up to China.”

Toward atomic arms status

A greater potential remains unspoken.

The nuclear fuel used for the submarines could accelerate South Korea’s path to “break out” as an atomic power, a status North Korea attained in 2006.

Seoul runs a sophisticated nuclear energy sector — it exports reactors — and the infrastructure and human resources that operate it, prerequisites giving it “nuclear latency:” The capability to develop a nuclear weapon.

But for decades, Seoul’s nuclear ambitions have been quashed by a proliferation-wary Washington.

The U.S. pressured it to shutter a clandestine nuclear arms program in the 1970s and has since bound the country into bilateral and international treaties.

Even so, Mr. Pinkston notes that from the 1980s to early 2000s, low-key and semi-secret domestic efforts have been suggested or operated: planning for submarine fuel plants, uranium enrichment, plutonium processing and laser enrichment.

“It is no surprise considering the tough ’hood they live in,” he said.

South Korea is overshadowed by nuclear-armed China, North Korea and Russia. Koreans are also wary of fellow democracy Japan for historical reasons.

Nuclear sub fuel, however, is not weapons-grade.

“You need enrichment of about 20% for a nuclear sub,” Mr. Pinkston said. “For a bomb, you want as high as you can get; 95%, or 80% percent with more core material.”

The process of generating fuel accelerates breakout potential.

“If you produce it yourself, you are that much closer to bomb-grade enrichment levels,” Mr. Pinkston said. “If you can make it to within the 20% level, you can make it up to 90%.”

Korea is newly empowered in those domains.

Mr. Lee announced Nov. 14 that the U.S. had expanded Korea’s uranium enrichment and fuel reprocessing authority.

“Throughout the talks, building our nuclear submarine in the U.S. was not discussed. The precondition of all conversations between the two leaders was that Korea’s nuclear submarine would be built in Korea,” National Security Adviser Wi Sung-lac told domestic media. “Our request for U.S. cooperation was focused on gaining access to nuclear fuel.”

Though Mr. Trump signaled that the boats would be made in the U.S., the Korean comments make sense.

The Pentagon has agonized over U.S. shipbuilding shortfalls, notably whether it is able to manufacture enough nuclear attack boats for not just the U.S. Navy, but also the Royal Australian Navy, per the AUKUS deal.

Mr. Yu added that although Korean shipbuilder Hanhwa Ocean has acquired a shipyard in Philadelphia, the yard is unsuitable for nuclear submarines.

Still, given the boats’ lengthy delivery timeline — which will outlive the Lee and Trump administrations — there is plenty of time for a rethink on both side of the Pacific.

“Nuclear submarine development requires reactor and fuel-cycle arrangements, a nuclear safety regulatory system, specialized crew training and major infrastructure investment,” Mr. Yu said. “Even with strong U.S.-[South Korea] cooperation … a first vessel in the late 2030s or early 2040s would be the most realistic window.”