• Lee, the South Korean president, announced a nuclear-powered submarine project after securing a bilateral agreement with the US.
• The program seeks to strengthen South Korea’s deterrence against North Korea’s growing nuclear threat.
• Though South Korea’s relationship with the US rapidly improved, this new alliance  strains relations with China.

Why is Lee HOT?

Answer: Lee’s nuclear-powered submarine project strengthens South Korea’s naval power and increases its regional deterrence, leaving him HOT.

Lee Jae-myung, South Korea’s president, announced on 26 May 2026 the launch of the “Jangbogo N Project”, a nuclear-powered submarine program, aimed at strengthening South Korea’s (ROK) naval power. The decision is expected to increase the nation’s deterrence capabilities in the region, contributing to Lee’s HOT rating.

Lee assumed office on 4 June 2025, and since then, he has worked on normalizing relations with North Korea. Despite efforts at de-escalation, relations with Pyongyang remain strained as Kim Jong-un continues to heavily invest in North Korea’s nuclear weapons programe, a threat that the ROK cannot overlook. The nuclear-powered submarine program seeks to counter this threat while also establishing  the ROK as a deterrent force.

However, it is important to note that Lee has no intent of developing a nuclear weapon but rather only improving the ROK’s military power. In fact, Seoul maintains a strategy of conventional sufficiency, meaning that it seeks to increase deterrence against North Korea through conventional military capabilities while upholding proliferation norms set by the International Atomic Energy Agency (IAEA).

Construction of the submarines will begin in the mid-2030s, with the vessels expected to enter service by the late 2030s. The project has a total estimated cost of 28.9 trillion won. Thus far, the ROK has moved beyond simple announcements and begun implementing the program. Seoul initiated the internal military procedures by launching bilateral US-ROK working groups focusing on developing low-enriched uranium fuel for nuclear-powered submarines, civilian uranium enrichment and spent fuel reprocessing. Nevertheless, the project complies with the ROK’s non-proliferation commitments by using low-enriched uranium fuel. 

Although construction has not yet begun, the development of the project has moved beyond mere campaign proposals into the implementation phase, thus strengthening Lee’s leadership position.

What is changing Lee’s heat level?

Answer: Amid tensions with China, Lee strengthened ties with the US, reinforcing South Korea’s deterrence.

Lee successfully turned a once weak US-ROK relationship into a strong strategic alliance that adds to his HOT heat level. At the start of Trump’s presidency, the US administration imposed tariffs on the ROK due to a large trade imbalance. Lee worked on reducing the trade imbalance while simultaneously securing economic and defence deals with the US. At the 2025 APEC summit on 1 of November 2025, the ROK and the US agreed to bilateral collaboration on civil uranium fuel development and the US approval process for South Korea’s construction of nuclear-powered attack submarines. This allows the ROK to strengthen its deterrence with new means of warfare. 

This shift also shows how the US will play a smaller role in deterring North Korea, transferring more responsibility to the ROK as it aims to transfer wartime operational control (OPCON) to South Korea by 2029, allowing Seoul to regain greater strategic autonomy on the Korean Peninsula.

Though the US represents a backbone for South Korean security, there is a trade-off: the ROK’s relationship with China. After his election in June 2025, Lee expressed that he wanted to restore diplomatic ties with China. Lee and Xi Jinping agreed to restore ties in a summit which took place in January 2026 paving the way for a “new phase” in bilateral relations. China is an important backer of North Korea; therefore, improving relations with China also supports Lee’s broader objective of reducing regional tensions involving North Korea. China has criticised the nuclear-powered submarine project, arguing that it risks undermining regional stability and contributing to an arms race.

The submarine plan resembles the nuclear-powered submarine cooperation established under the US, UK, and Australian AUKUS alliance. According to China’s Foreign Ministry, the submarine program threatens regional stability, prompting Beijing to call on the US and South Korea to fulfil their non-proliferation obligations and act in ways that support regional peace. However, China does not fully condemn the plan. The Chinese reaction was not as strong as the reaction it had regarding AUKUS, which the Chinese government strongly opposed, signalling a desire to preserve a positive relationship with Lee.

What is driving Lee?

Answer: Lee’s pragmatic approach regarding political and economic policies is what drives him to implement the Jangbogo-N project.

Lee’s leadership and actions display a sense of political pragmatism when it comes to his goal: achieving de-escalation with North Korea. He first attempted to open discussions to resolve the issue diplomatically through the END framework: Exchange, Normalization, and Denuclearization which was rejected by North Korea. To regain leverage in the Korean Peninsula, he recalibrated his approach and invested in defence by implementing the nuclear-powered submarine program: a shift in approach that reflects his pragmatism.

As well as in politics, Lee also demonstrates his pragmatism in the economic sector. Lee seeks to secure the US both as an economic and security partner. Seoul pledged $350 billion in tariff-relief investment, a costly concession, restoring the US-ROK relationship while securing the submarine project and the transfer of OPCON. As part of South Korea’s commitment to help the US economy, Hanwha Group announced a $5 billion infrastructure plan for Hanwha Philly Shipyard.

Domestically, the project also aims to create economic growth and generate jobs for Hanwha Ocean, HD Hyundai Heavy Industries, and suppliers in navigation, batteries, and precision components, while strengthening Korea’s hand in export competition. The project is expected to generate approximately 40,000 jobs in South Korea. The economic benefits allow the ROK to frame the project both as a security issue and as an opportunity for economic growth, strengthening Lee’s position.

What does this mean for you?

Answer: Lee’s program creates a precedent that may encourage other non-nuclear states to seek similar enrichment and reprocessing arrangements.

Though Lee’s Jangbogo-N project respects the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) and the IAEA’s guidelines, it still creates a precedent that could weaken the global non-proliferation regime. To refrain from moving towards nuclear weapons, South Korea’s Defence Ministry is moving to prohibit nuclear fuel intended to power submarines from being diverted to nuclear weapons; this reduces the risk of nuclear escalation during periods of heightened tension. However, if a non-nuclear state such as South Korea can secure US-backed enrichment and reprocessing rights by invoking submarine propulsion, other states may follow that example, placing additional strain on the global non-proliferation regime.