South Korean SLBM – between narratives and broader consequences

By – Pawel Behrendt

In recent weeks media from South Korea informed about two successful tests of submarine-launched ballistic missile (SLBM). Without any doubt, it is a huge win; Republic of Korea has joined an exclusive club of states with the “second strike” capability; furthermore, it is the sole non-nuclear state in this group. Nonetheless, the missile success brings forward many questions of strategic and geopolitical consequences.

According to media reports, the SLBM was test-fired from Dosan Ahn Chang-ho conventional submarine, the prototype vessel of the KSS-III class, which was commissioned in August this year. The KSS-III is distinguished from other conventional submarines by six K-VLS vertical launchers for the Hyunmoo-4-4 ballistic missile and Hyunmoo-3C cruise missile with a range of 1,500 kilometres. However, the ROK Navy decided that six launchers were not enough to create a credible deterrent system; hence, the ships of the second tranche are to receive more K-VLS, with the figure of ten most often mentioned in the media.

The ROK Ministry of National Defence has refused to confirm the details for security reasons; however, neither the tests nor the missile capabilities of the submarine were a surprise. Reports emerged in early July that South Korea launched the same type of SLBM from a submerged barge. Back then, the Naver portal had suggested that a test firing of a rocket from Dosan Ahn Chang-ho could take place soon. During the first September test, a missile was just ejected from a submerged vessel; two weeks later, it was launched.

The type of tested missile is not known, but most sources point to a modified version of the Hyunmoo-2B tactical ballistic missile with a range of 500 kilometres. The development of an indigenous SLBM was initiated in 2013 after North Korea conducted its third nuclear test, and intelligence obtained the first information on an analogous missile north of the 38 parallel. The program was dubbed K-SLBM. Seoul officially revealed work on the missile in July 2017. This came after Pyongyang conducted its fifth nuclear test and successful tests of Pukguksong-1 and -2 SLBMs.

Further information about the K-SLBM emerged this spring. The military research and development agency Daejeon Sejong Research Institute (DSRI)is said to be working on three types of ballistic missiles derived from the Hyunmoo-2B and designated Hyunmoo-4. The Hyunmoo-4-1 is said to be for ground forces and designed to destroy North Korean bunkers and underground command posts; meanwhile, the Hyunmoo-4-2 is a ballistic missile for surface ships while the Hyunmoo-4-4 is the K-SLBM. No information is available on the Hyunmoo-4-3, and there is speculation that it may be a hypersonic missile.

South Korea’s ballistic missile journey

This is not the end of Seoul’s ambitions. The medium-term defence plan for the current decade, announced in August 2020, envisages the development of a new generation of submarines with a displacement of 3600-4000 tonnes carrying ballistic missiles. Both conventional and nuclear propulsion has to be under consideration. South Korea has been considering the construction of nuclear-powered vessels since 2003, but so far, technical and financial problems, as well as pressure from Washington, have stood in the way.

The US for years had curbed South Korea’s ballistic missile ambitions; the 1979 US-ROK military agreement limited the range of missiles to 180 kilometres. At the time, the United States intended to limit South Korea’s ability to attack targets north of Pyongyang and thus to deescalate tensions in the Korean Peninsula. These assumptions ceased to be valid with the development of North Korea’s missile programme. However, the agreement itself was not renegotiated until 2001, when the range of South Korea’s ballistic missiles was increased to 300 kilometres, while the maximum weight of a warhead remained at 500 kilograms.

In fact, the main concern of military planners in Seoul was the latter parameter. It was felt that a half-ton warhead would not provide adequate capability against North Korean bunkers and underground installations. Hence, in the next round of negotiations, South Korea demanded to increase the range of missiles to 1,000 kilometres and the weight of warheads to one tonne. However, the administration of President Barack Obama only agreed to increase the range to 800 kilometres. It was only in 2017 that President Donald Trump, ‘in-principle’, agreed to increase the warhead weight to one thousand kilograms.

Nonetheless, throughout such negotiations spanning years, South Korea was not discouraged. The range restriction was circumvented by introducing the Hyunmoo-3 cruise missiles, which are not covered by the treaty. It is also known that the already mentioned Hyunmoo-2 family missiles can carry 1,000-kilogram warheads, but this reduces their range. According to unconfirmed information, the Hyunmoo-4 missile can carry a warhead weighing up to 2 000 kg.

Finally, President Biden’s administration in May 2021 agreed to lift  all restrictions on South Korea’s ballistic missiles. Undoubtedly, Washington’s agreement is a major success for South Korean diplomacy. It is currently difficult to assess to what extent the decision to lift restrictions on South Korea’s ballistic missiles is related to the United States’ 2019 denunciation of the Intermediate-Range Nuclear Forces Treaty (INF). On the other hand, Seoul has announced that it does not intend to develop or deploy ballistic missiles with a range of over 800 kilometres.

Gauging Seoul’s outlook on SLBM’s

The reason for such a restrained approach is simple: Korea wants to avoid a missile arms race in East Asia. With a range of 800 kilometres, Hyunmoo-2C ballistic missiles, which are probably deeply modified Russian Iskander tactical ballistic missiles, can strike any target within North Korea. Such capabilities are a priority for South Korean planners. However, western Japan and parts of China and Russia are also within range of the Hyunmoo-2C. The Hyunmoo-3C cruise missiles have a range of 1,500 kilometres, and for the moment, their deterrence potential is considered sufficient.

The ROK leadership is aware that the development and introduction of medium- and/or intermediate-range ballistic missiles could provoke a response from China and Russia. Therefore, ROK carefully observes Beijing’s and Moscow’s reaction to its ballistic missile programme development. Another restraining factor is Japan. South Korea’s ballistic missiles would definitely deliver arguments to advocates of the idea that the Self-Defence Forces (SDF) should acquire the ability to strike enemy bases that threaten the country’s security. Such a step by Tokyo would definitely tilt the balance of power in North-East Asia and make an even greater contribution to the arms race in the region. As of now, none of the neighbouring powers expressed concern about the K-SLBM program, at least officially.

The lifting of the restrictions has, of course, provoked criticism from Pyongyang. The communist regime may fear a costly arms race that it will not be able to sustain. This fear was reflected when the Korean Central News Agency (KCNA) –North Korea’s state media – accused Seoul and Washington of stimulating an arms race on the Korean peninsula and seeking to impede North Korea’s development. 

Despite such directives, K-SLBM program remains somewhat puzzling. The growing range of ballistic and cruise missiles, as well as submarines armed with such weapons, speculate about Seoul’s ambitions to build capabilities enabling power projection not only in Northeast Asia but also the Indo-Pacific –even as South Korea remains wary of endorsing the Indo-Pacific concept. Such divagations are fuelled by the decision to build an indigenous light aircraft carrier.

However, South Korean official sources are clear: the range of ballistic missiles will be limited to 800 km. As pointed earlier, the ROK military is mainly interested in larger warheads able to destroy North Korean bunkers and underground command posts. The deterrence is aimed predominantly on the northern neighbour and presumes using ballistic and cruise missiles to eliminate North Korean leadership, command chain and crucial installations. Submarines armed with missiles are another asset strengthening the deterrence and enabling the second strike. Another reason to introduce such complicated systems is the simple fact that North Korea is doing the same. Also, under Moon-Jae In, South Korea has been actively trying to build itself as a strong, if not formidable, middle power; initiatives like the ‘New Southern Policy’ and Korean ‘New Deal’ have shown Seoul’s attempts to engage with neighbours and lead by example.

On the other hand, the South Korean deterrence may be in the longer perspective aimed at China and Japan. Given sour relations with both states and uncertainty about the US commitments, such an option seems valid. It raises, however, the question of the credibility of such a non-nuclear deterrence. Missiles with conventional warheads may not be necessarily effective to deter nuclear powers like China and North Korea.

An uncertain future

Does the ROK aim to go nuclear? Such a discussion has been going on since North Korea’s nuclear programme began. Proponents of this solution stress that the best way to deter a nuclear-armed enemy is to acquire its own nuclear weapons. They warn of the risk of becoming a political hostage to Pyongyang once it has successfully completed its nuclear and missile programmes. Another argument concerns the reliability of the US nuclear umbrella. 

Opponents of acquiring nuclear weapons warn of the risk of a domino effect and the unleashing of a regional nuclear arms race. The biggest concerns here are the reaction of China and the fear of Japan deciding to develop its own nuclear weapons. In such a situation, Pyongyang would also gain justification for its actions. In addition, ROK would have to withdraw from the Non-Proliferation Treaty, which could undermine its position in the international arena and, in extreme cases, expose it to sanctions.

The decision to respond to North Korea’s SLBM programme has given the ROK new capabilities and options. As of now, Seoul remains concentrated on Pyongyang and does not declare broader ambitions. However, this posture may change with the evolution of the geopolitical situation. Actions taken by Washington, Beijing and Tokyo, as well as ambitions of Korean leadership, are poised to shape the security arc of the region.

Pawel Behrendt is a Political Science PhD candidate at the University of Vienna. He is a Member of the Board at the Boym Institute in Warsaw and is a regular contributor to

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