U.S. Approves South Korea’s Nuclear Submarine Construction on American Soil

In a major geopolitical and defense breakthrough, U.S. President Donald Trump announced on October 29th that the United States has granted approval for South Korea to build nuclear-powered submarines on U.S. soil. The revelation came during a high-profile meeting between Trump and South Korean President Lee Jae-Myung in Gyeongju, followed by posts on Trump’s Truth Social account confirming that construction will take place at Philadelphia Shipyards, now owned by Hanwha Ocean, a leading South Korean defense firm.

This decision marks a historic shift in U.S.–South Korea defense cooperation, as it will be the first time South Korea constructs nuclear submarines, and notably, the first such project hosted on American territory.

A Long-Awaited Green Light

South Korea’s interest in nuclear-powered submarines dates back more than a decade, but it was formally requested from the United States in 2016 during the administration of President Park Geun-hye. The request resurfaced in 2018 and again in 2021, under Presidents Moon Jae-in and Yoon Suk-yeol, as North Korea accelerated development of submarine-launched ballistic missiles (SLBMs) and expanded its own underwater nuclear deterrent.

Until now, the U.S. had refrained from granting permission due to nuclear proliferation concerns under the U.S.–ROK Atomic Energy Agreement, which limits South Korea’s ability to use enriched uranium for military purposes. However, mounting regional security challenges — including China’s assertive naval posture and Russia’s Pacific rearmament — shifted the U.S. stance.

President Trump, seeking to demonstrate renewed American leadership and allied empowerment, finally gave the “go-ahead” in late October, stating:

“Our (U.S. and South Korea’s) military alliance is stronger than ever before, and based on that, I have given them approval to build a Nuclear Powered Submarine.”

This approval effectively unlocks a project that has been stalled for nearly nine years, representing the culmination of persistent South Korean diplomacy and strategic alignment between Washington and Seoul.

Project Location and Hanwha’s $5 Billion Investment

The project will center around the Philadelphia Shipyard, a facility historically used for commercial shipbuilding rather than military nuclear work. After Hanwha Group acquired a controlling stake in late 2024, the company pledged to invest over $5 billion to modernize and adapt the facility for submarine construction.

According to U.S. defense officials, Hanwha’s modernization plan will include:

• Establishment of nuclear handling infrastructure,

• Creation of shielded assembly halls and pressure hull manufacturing lines, and

• Recruitment of U.S. and South Korean engineers specializing in nuclear propulsion systems.

However, as of late October, no formal intergovernmental memorandum of understanding (MoU) has been signed, and the final project blueprint remains under negotiation between Seoul’s Defense Acquisition Program Administration (DAPA) and the U.S. Department of Defense.

Estimated Cost and U.S. Role

Preliminary estimates place the total project cost at $15–18 billion USD, covering shipyard upgrades, reactor development, and submarine construction for an initial fleet of four to six vessels.

The U.S. contribution will primarily involve:

• Reactor safety certification and nuclear technology oversight,

• Access to enriched uranium supply chains under defense exemptions, and

• Integration of U.S. sonar and combat management systems into the final submarine design.

This arrangement ensures non-proliferation compliance while still granting South Korea a pathway to develop indigenous nuclear propulsion technology under close American supervision.

South Korea’s Strategic Vision

South Korea’s Navy, or ROKN, envisions the nuclear submarine as a deterrent platform with global operational endurance — capable of tracking North Korean missile submarines and maintaining stealth patrols deep into the Pacific.

During the National Assembly’s Defense Committee audit on October 30th, Chief of Naval Operations Admiral Kang Dong-gil stated:

“The start date for the nuclear-powered submarine program has not yet been decided, but once it begins, it will take more than 10 years. Its displacement is expected to exceed 5,000 tons.”

DAPA Commissioner Seok Jong-geon added that based on comparisons with “advanced countries,” it typically takes a decade to build an SSN, but South Korea’s strong industrial base could shorten the timeline.

Defense Minister Ahn Kyu-baek hinted at a fleet size goal of at least four nuclear submarines, forming the backbone of South Korea’s underwater deterrence strategy.

Design and Technological Foundation

South Korea’s KSS-III (Dosan Ahn Changho-class) submarine is widely believed to serve as the base platform for nuclear adaptation.

The KSS-III, already the first fully indigenous South Korean submarine, weighs 3,750 tons (Batch I) and up to 4,200 tons (Batch II). It features:

• K-VLS (Korean Vertical Launch System) cells — six on Batch I, ten on Batch II,

• Advanced AIP (Air Independent Propulsion) system,

• Modern combat systems and sonar suites developed by Hanwha Systems.

Defense experts suggest that a nuclear variant of the KSS-III, with a reactor module replacing the AIP system, could reach 5,000–5,500 tons, offering extended underwater endurance and higher sustained speeds — key for long-range patrol and anti-submarine warfare operations.

Strategic and Industrial Implications

This cooperation represents a major win for both nations.
For the United States, it strengthens a trusted naval partner in the Indo-Pacific — one capable of independently countering growing Chinese maritime influence and deterring North Korean aggression.

For South Korea, it finally achieves a long-standing defense goal — joining the elite circle of nations operating nuclear-powered submarines, alongside the U.S., U.K., France, Russia, India, and China.

Moreover, by choosing U.S. soil for construction, both sides ensure tight control over nuclear materials and prevent proliferation concerns, while boosting American shipbuilding employment through joint industrial integration.

The U.S. approval of South Korea’s nuclear submarine program marks a historic milestone in the evolution of the U.S.–ROK alliance. While the path ahead involves years of planning, engineering, and regulatory coordination, the decision alone reshapes the strategic balance in the Indo-Pacific.

Once completed, these submarines will not only symbolize South Korea’s technological maturity but also embody a new model of allied defense cooperation — one built on shared deterrence, industrial synergy, and trust between two of the world’s closest partners.

In essence, the Philadelphia-built nuclear submarines may soon become the ultimate emblem of the U.S.–South Korea alliance in the 21st century.