South Korea has announced plans to develop a new nuclear-powered submarine, named Jang Bogo-N after a famed 9th-century naval commander. The move is seen as a strategic effort to counter North Korea’s ongoing pursuit of similar capabilities and is expected to escalate the military competition on the Korean Peninsula.

The Jang Bogo-N, which builds on South Korea’s previous diesel-electric submarine program initiated in the 1990s, aims to significantly enhance Seoul’s naval strength. Nuclear-powered submarines offer advantages over conventional ones, including higher speed, quieter operation, and extended underwater endurance, which could alter regional maritime dynamics amid rising geopolitical tensions.

Analysts highlight that the deployment of such vessels would complicate the strategic calculations for North Korea and other potential adversaries in the region. Peter Ward from the Sejong Institute in Seoul described the development as a marked upgrade in South Korea’s naval capabilities, potentially improving the country’s ability to monitor North Korean and Chinese submarine activity.

North Korea has been ahead in publicizing its nuclear submarine ambitions, unveiling the hull of its first nuclear-powered submarine in 2025. Pyongyang views these vessels as critical to establishing a "second strike" nuclear deterrent, one that could operate farther into the Pacific and threaten locations including Guam and Hawaii. However, experts remain uncertain whether North Korea has successfully developed the necessary nuclear propulsion technology. Moon Geunsik, a former South Korean submarine commander, noted that while the submarine hull has been revealed, confirmation of a functioning reactor remains unverified.

In 2023, North Korea introduced the Hero Kim Gun Ok, a diesel-electric submarine modified to carry nuclear-capable ballistic and cruise missiles, although no evidence suggests it has entered full operational service.

Some analysts caution that North Korea could acquire missing technology through strengthened military ties with Russia, especially amid Pyongyang’s support for Moscow in the Ukraine conflict. Kim Yeol-soo of the Korean Institute for Military Affairs noted that North Korea might request nuclear propulsion systems from Russia or attempt to obtain technology via cyber espionage, citing their advanced hacking capabilities.

South Korea, in contrast, demonstrates clear technical capacity to produce nuclear-powered submarines, drawing on its established expertise as a major exporter of civilian nuclear reactors and builder of diesel-electric submarines. However, past efforts to develop nuclear subs were blocked by the United States, as Seoul is bound by agreements requiring Washington’s approval to handle uranium enrichment or reprocessing needed for naval reactors.

This impasse shifted following a 2025 visit to South Korea by then-US President Donald Trump, who publicly endorsed Seoul’s nuclear submarine program. Trump announced on social media that he had granted approval for South Korea to build nuclear-powered submarines, a departure from previous US policy. Despite this, some experts express doubt about the feasibility of the plan as initially described. Trump’s social media posts indicated the submarines would be constructed at the Philadelphia Shipyard in the United States, which, despite recent acquisition by South Korean conglomerate Hanwha, has no submarine-building experience. Ankit Panda of the Carnegie Endowment for International Peace warned that this mismatch of expectations could lead to future complications.

South Korea’s presidential office and defense ministry have not commented publicly on these developments. President Lee Mayung asserted that nuclear-powered submarines would enhance South Korea’s ability to monitor regional threats, particularly from North Korea and China, potentially easing the operational burden on US forces in the area. Some South Korean analysts suggest that Seoul should emphasize its strategic role in containing China in collaboration with the United States.

China’s government has advised South Korea to approach US cooperation on nuclear submarines cautiously, reflecting Beijing’s concern about shifting security dynamics. Meanwhile, the continued expansion of China’s own submarine fleet remains a source of apprehension for Washington and its regional allies.