Technical Features and Operational Implications of the ROK Navy’s New Class of Submarines

Introduction

Rising tensions in the East and South China Seas and across the Taiwan Strait have sparked a rush of submarine production around East Asia. Taiwan launched its first domestically built submarine, the Hai Kun, in September 2023,[1] and Japan launched its fourth Taigei-class submarine, the Raigei, in October 2023.[2] South Korea, meanwhile, added the third Dosan Ahn Changho-class submarine to its fleet with the commissioning of the Shin Chaeho on April 5, 2024.[3]

The Dosan Ahn Changho-class submarines are the products of South Korea’s KSS-III program and are marked by major technological advances over earlier vessels. The advances suggest that the security environment surrounding South Korea now require new operations. In the following, I will provide an overview of the technical features of the Dosan Ahn Changho-class submarines and consider their operational implications.

Technical Improvements under the KSS-III Program

The Republic of Korea Navy (ROKN) began full development of its conventionally powered submarine fleet in the 1990s. Under the initial KSS-I program, nine Jang Boho-class submarines were built under license based on the German Type 209 design. The subsequent KSS-II program resulted in the licensed production of nine Son Won-il-class submarines based on the German Type 214. By 2018, the ROKN had 18 operational submarines. For the KSS-III phase, South Korean manufacturers are undertaking the entire construction process, from design to production. Nine KSS-III submarines are being built from 2021 in three batches of three vessels each, with design improvements being planned at each stage.[4] The ROKN currently has 21 submarines,[5] but the aging Jang Boho-class submarines are expected to be gradually retired as the KSS-III phase progresses.

When compared to the KSS-II, the KSS-III features three major improvements. The first is size. The hull of the Son Won-il class was 65 meters long, while the Dosan Ahn Changho class measures 83.5 meters. There has also been a significant increase in displacement from 1,800 tons to 3,700 tons. The larger hull means more room for the crew and supplies, enabling long-term operations over vast distances in the open seas.[6] This, though, raises the question of why a need was felt to overcome operational constraints and achieve upgraded capabilities.

The second improvement is in the propulsion system that enhances underwater operations. Like the Son Won-il class, the Dosan Ahn Changho class uses diesel batteries and fuel cells, but thanks to domestic production of fuel cells and performance improvements, the submerged endurance[7]of the Dosan Ahn Changho class has been extended by more than a week to 20 days.[8] This, along with the improvements mentioned above, has expanded the operational range and period of conventionally powered submarines.

The third improvement is in ground-strike capabilities. In addition to torpedo tubes like those on previous vessels, the Dosan Ahn Changho-class submarines are equipped with a vertical launch system (VLS) that can fire submarine-launched ballistic missiles (SLBMs) at land targets. The new design will accommodate the Hyunmoo 4-4—an upgraded version of the Hyunmoo 2B surface-to-surface ballistic missile—with a range of approximately 500 kilometers and payload of approximately 1 ton.[9] South Korean SLBMs are sometimes discussed in terms similar to a Cold War nuclear deterrence strategy, as they give the country a so-called second-strike capability—which ordinarily means the ability to respond to a nuclear attack with powerful nuclear retaliation against the attacker. Of course, such a capacity would first require the possession of nuclear warheads, but the very fact that South Korea can now launch SLBMs suggests a change in the objectives of the ROKN’s submarine operations.

Operational Objectives of the Dosan Ahn Changho Class

Generally speaking, submarines are designed to meet such objectives as maritime control, reconnaissance and surveillance, anti-surface warfare, anti-submarine warfare, land attack, special warfare, and minelaying.[10] Of these objectives, South Korean submarines have focused on tactical operations, such as reconnaissance and surveillance and minelaying.[11] Given that North Korea has a powerful ground force but a weak navy, there had been little need for the ROKN to possess a large fleet of high-performance attack submarines. The task of searching for North Korean submarines was mainly assigned to coastal sonar systems and naval aviation units, rather than hunter-killer submarines.[12] Thus the deployment of small submarines of under 2,000 tons, with short periods of continuous underwater operations and armed with just torpedoes and mines had been a rational allocation of resources. The technological improvements of the Dosan Ahn Changho class and the cost of achieving them point to a need to meet new operational requirements.

The larger hull and extended submerged endurance are no doubt intended to enable longer-term operations. This, though, is not essential considering the relatively narrow operational area of the ROKN.[13] And since North Korea has almost no means of detecting submarines,[14] there is no need to remain submerged when operating far from the coast. What prompted the development of new capabilities is the introduction of SLBM-equipped submarines by North Korea.[15] To monitor the entry and exit of these vessels from military ports and to track and attack them if necessary, new submarines were needed that could remain undetected in front of enemy ports for long periods of time.

The reasons for the acquisition of SLBM capability, meanwhile, are believed to be twofold. The first, as made clear in the 2022 defense white paper, is as part of the Korea Massive Punishment and Retaliation (KMPR) strategy under South Korea’s 3K Defense System to counter any large-scale attack from the North.[16]The SLMBs’ role in this system, though, is considered rather limited, since initial wartime strike targets are determined by the Army and Air Force. There have been no simulations of submarines striking land targets, moreover, in recent joint exercises with the US military.[17] At most, the SLBMs will ensure the survival of limited retaliatory capability in the case of a massive North Korean attack. They are not needed to attack SLBM-equipped North Korean submarines, so it would be difficult to justify the possession of SLBMs solely as a component of KMPR.

The second reason for operating SLBMs must be discerned from reading between the lines of the defense white paper. North Korea is the only country that is identified as the “enemy” in the document, but there is a change in strategic awareness between the 2020 and 2022 editions. Until 2020, the stated national security strategy was to take the initiative in the pursuit of a peaceful and prosperous Korean Peninsula in cooperation with countries in the region,[18] but in 2022, the focus shifted to defending and promoting the universal values of freedom, democracy, and human rights on the Korean Peninsula and the surrounding region.[19] Particularly noteworthy are clear references to “threats” other than North Korea and to the strategic competition between the United States and China.[20] Interestingly, a European expert points out that South Korean SLBM operations are aimed at projecting force throughout the Indo-Pacific and have implications for the region’s balance of power.[21] Given the possibility that the hands of the South Korean Army and Air Force may be tied in the event of a Korean Peninsula contingency, it is only natural to consider the use of high-stealth SLBMs to address potential threats.

In Conclusion

New strategic and operational objectives and needs give rise to new weapons systems. But the dilemma this creates is that such new capabilities will raise concerns in other countries and could trigger an arms race. There is no refuting the fact that the primary purpose of South Korea’s SLBMs is to deter North Korea, but neighboring countries may see other reasons. China, for one, has criticized the United States of using a double standard in allowing South Korea to possess SLBMs.[22] A Taiwanese think tank, meanwhile, argued that the SLBMs will lead to changes in China’s Northern Theater Command and could result in a balancing of military power against Taiwan.[23] There is also research that sees SLBM deployment as a signal not just to Pyongyang but also to Washington that Seoul may embark on nuclear weapons development.[24] Although the true intentions of the South Korean government remain unclear, the current program to secure nine SLBM-equipped submarines has doubtless become a significant factor that must be considered when thinking about the region’s security environment.