The case for nuclear-powered submarines

A submarine is a military or civilian vessel designed to operate underwater for extended periods, capable of diving below the surface, navigating while submerged and resurfacing at will. Its defining feature is the ability to function effectively in three dimensions — on the surface, at periscope depth and in deep water. The first military use of a submarine in combat was in 1776. It was called the Turtle and was used by the American Continental Army during the Revolutionary War. The first successful submarine attack was in 1864. The Confederate submarine CSS Hunley sank the USS Housatonic during the U.S. Civil War.

During World Wars I and II, submarine operations became a critical part of naval warfare. German submarines, known as U-boats, are infamous for their role in disrupting naval operations and exerting significant strategic impact. On the Korean peninsula, North Korea focused on building a naval force with a vengeance after the Korean War. Focusing on a littoral force, the North Korean navy concentrated on a fleet of submarines that were initially imported from the Soviet Union and the People’s Republic of China. South Korea started building small submersibles in the 1970s and began to build its fleet from a German design, which became operational in 1992. Today, South Korea has indigenous heavy submarines with submarine-launched ballistic missile (SLBM) capability. Both Koreas have their own design of torpedoes.

Nuclear-powered submarines began with U.S. research in the late 1940s. The USS Nautilus (1955) was the transformational breakthrough. The U.S. and USSR built massive fleets during the Cold War and the capability later spread to the UK, France, China and India. Today, nuclear submarines remain a core strategic deterrent and a sea-control asset. North Korea has publicly stated that it will build not only a nuclear-powered submarine but a nuclear-armed submarine. Against this backdrop, South Korea has been researching submarines for over 30 years, and during the 57th Security Consultative Meeting, it asked the U.S. for cooperation to build a nuclear-powered submarine, which has spurred much controversy in Korea.

China has expressed concerns about nuclear proliferation and North Korea sees South Korea’s nuclear-powered submarine initiative as part of a broader U.S.-ROK strategy to degrade or threaten the North’s security. In reaction, the North has voiced strong condemnation, pledged to expand its own nuclear and submarine ambitions, and warned of retaliatory or “offensive” measures. Critics in South Korea cite cost and the reliance on U.S. technology, which they say will lead to perpetual dependence on the United States. It may be an unusual perspective, but this is a free country.

South Korea operates one of the world’s most reliable, safest and most efficient civilian nuclear power programs. The Korean APR-1400 reactor is certified by the U.S. Nuclear Regulatory Commission and the European Utility Requirements. Korea successfully exported complete nuclear power plants (UAE Barakah units 1–4), a feat achieved by only a handful of countries. On the other hand, South Korea lacks uranium enrichment capabilities due to nonproliferation agreements with the U.S., does not conduct full plutonium reprocessing and has no operational nuclear submarine program, although it has studied small reactors for surface ships and submarines — but nothing is deployed. Here is where South Korea needs U.S. help.

With assistance from the United States, South Korea’s nuclear-powered submarines could mark the start of research that would advance peaceful nuclear technology. The marriage of U.S. and Korean technology in Small Modular Reactors (SMRs) is expected to have a profound impact, providing a versatile energy source for powering artificial intelligence as well as numerous applications in daily life. The benefits of SMRs are: higher safety margins through passive/underground designs; lower capital costs and financial risk; scalable deployment that grows with demand; smaller land and water footprint with flexible siting; compatibility with renewables; capability for process heat; and options for remote, industrial and military use.

South Korean nuclear-powered submarines will also play a key role in protecting global supply chains. Once the Arctic route opens, submarines with extended endurance will be especially important. This role will begin in the Korea Straits and extend to the Arctic, safeguarding trade between Europe and Asia.

Ultimately, the development of nuclear-powered submarines will provide South Korea with the foundation for a credible second-strike deterrent — ensuring survivability, persistence, and operational flexibility even in the event of a first strike. A nuclear-powered submarine fleet, with the ability to remain submerged for extended periods, operate covertly in distant waters and maneuver without dependence on air or surface support, would dramatically increase the resilience of South Korea’s strategic posture. By denying adversaries the confidence that a surprise attack could neutralize their national defenses, this capability strengthens deterrence, complicates enemy planning and reduces the risk of miscalculation. In this sense, nuclear-powered submarines would not only enhance battlefield advantages but would also contribute directly to national security, alliance interoperability and long-term stability on the Korean Peninsula.

In an era defined by nuclear coercion, regional instability and contested sea lanes, a South Korean nuclear-powered submarine capability is not a luxury but a strategic necessity. It would reinforce deterrence by ensuring secure second-strike capability, enhance maritime endurance for protecting global trade routes including, future Arctic passages, and deepen alliance-based technological integration rather than dependence. Paired with Korea’s world-class civilian nuclear expertise and U.S. partnership, such a program would accelerate innovation in advanced reactor technology with civilian applications far beyond defense. Ultimately, pursuing nuclear-powered submarines reflects South Korea’s right and responsibility to protect its people, secure its economy and contribute to regional and global stability.

Retired Lt. Gen. Chun In-bum is the former commander of the Republic of Korea Army Special Warfare Command.