South Korea's stealth quest for a nuclear triad

A nuclear triad consists of land, sea, and air delivery systems for nuclear weapons. These include SLBM missiles carried by submarines, ballistic missiles stationed on land in silos or on mobile launchers, and aerial weapons in the form of bombs or cruise missiles carried by aircraft.

Only some nuclear powers, such as the United States, Russia, China, and India, possess a full triad. Some countries—like France or the United Kingdom—intentionally limit their nuclear arsenals. Others—like Pakistan or North Korea—are still attempting to build a complete range of nuclear weapons types.

A country that is consistently moving in this direction is also South Korea. Although Seoul lacks its own nuclear weapons, it is developing delivery systems that—once equipped with nuclear warheads—will provide it with access to a full nuclear triad.

In August 2021, the first KSS-III class submarine, also known as Dosan Ahn Changho due to the first ship, entered service in the South Korean navy. This submarine is a 276-foot unit displacing about 4,078 tons underwater. Alongside diesel propulsion, the submarine also has fuel cells, allowing it to operate for 20 days without needing atmospheric air.

The KSS-III type was initially designed as a carrier of SLBM missiles. The first batch of this type of submarine includes six vertical launch pads located behind the sail, in addition to torpedo launchers. Currently, they house Hyunmoo 4-4 ballistic missiles with a range of about 311 miles. The second batch of slightly enlarged KSS-III submarines will have 10 launchers, accommodating both ballistic and cruise missiles.

South Korea plans to build nine KSS-III type submarines. Seoul's plans also include developing another type of submarine, specifically designed to carry ballistic missiles. One of the options considered for this variant is nuclear propulsion.

Although South Korea's achievements in developing ballistic missiles are more modest than those of its northern neighbor, Seoul also possesses ballistic missiles with ranges that have increased with each new development version of this weapon.

In the 1980s, the Hyunmoo-1 ballistic missile with a range of 112 miles (limited due to US pressure) entered service. Since 2008, the Hyunmoo-2 missile family has been developed, with different variants having ranges from 186 to 497 miles.

Various variants of Hyunmoo-3 missiles, carrying relatively light, 1,102-pound warheads, have ranges from 311 to 932 miles.

The Hyunmoo-4 missiles, tested since 2020, have a range of 497 miles but carry very heavy warheads weighing about 4,409 pounds. They feature extremely high accuracy, with a circular error probable of 1-2 meters. These missiles are intended to destroy North Korean bunkers using conventional warheads.

In October 2024, South Korea unveiled another missile—the Hyunmoo-5, capable of carrying an 8-ton warhead over a distance of 1,864 miles.

A range of 497 miles is sufficient to destroy any target within North Korea; hence, South Korea's ability to target increasingly distant objectives has drawn criticism, particularly from Tokyo and Beijing.

South Korea has aerial cruise missiles but currently imports Taurus missiles. Seoul ultimately wants to develop its own weapon of this type, as evidenced by the Cheonryong (Korean: heavenly dragon) missile displayed in September 2021.

Although the Cheonryong was carried by an old F-4 aircraft during a test, the missile, with a range of 621 miles, was developed as part of the domestic aerial arsenal intended for the future KF-21 Bormae aircraft, significantly enhancing its strike capabilities.

Another long-range aerial weapon was unveiled by South Korea in October 2024 during the 2024 Sacheon Airshow. Among the displayed weapons was a mockup of an aerial missile currently under development with a ramjet engine, intended for KF-21 and FA-50 aircraft. The missile is expected to travel at a speed of Mach 3.5 and offer a range of 186 miles.

In the 1970s, South Korea conducted efforts aimed at acquiring nuclear weapons. These efforts were halted due to international pressure, mainly thanks to US intervention. In 1975, Seoul ratified the Treaty on the Non-Proliferation of Nuclear Weapons.

Nevertheless, as revealed years later, South Korean researchers successfully conducted experimental enrichment of small amounts of uranium to levels suitable for military application, as part of a secret experiment.

Washington's pressure also limited the development of South Korean ballistic missiles. Until the mid-2010s, they could carry warheads weighing up to 1,102 pounds over a distance of up to 497 miles. The lifting of these restrictions in 2017 resulted in the emergence—within just a few years—of a family of increasingly heavier ballistic missiles with increasing ranges.

The price for Seoul's abandonment of work on a nuclear arsenal involved not only American security guarantees but also the stationing of American nuclear weapons on South Korean territory. At the turn of the 1980s and 1990s, there were even 950 bombs, although these were later withdrawn from Korea.

In 2023, during a meeting with the heads of the defense and foreign affairs departments, President Yoon Suk announced that—if the threat from North Korea continues to grow—South Korea might consider inviting the US to redeploy nuclear warheads on its territory or develop its own nuclear weapons. An agreement made in the same year between Seoul and Washington permits the stationing of American submarines with nuclear weapons on board in Korea.

According to research conducted in 2023, over 70% of South Korean residents support the development of their own nuclear weapons. Given that South Korea is a world leader in nuclear energy, boasting extensive industrial and research facilities, it is not a lack of capability that restrains it from building a nuclear arsenal, but the political consequences of such a move.