During US President Donald Trump’s recent visit to Seoul, he reportedly discussed the possibility of South Korea acquiring nuclear-powered attack submarines (SSN) with President Moon Jae-in. According to one South Korean official, Seoul might purchase the boats from the US or build them on its own, but in either case, there were many technical issues to iron out and a final agreement will take time.
South Korea has considered this possibility in the past. Defence planners are concerned with North Korea’s ambitions to develop a submarine capable of firing ballistic missiles that could carry nuclear warheads; SSNs would be an answer to this challenge. But while SSNs would provide the South Korean Navy with a highly capable asset, the potential gain is small and not worth the cost.
South Korea’s current submarine force consists of nine Chang Bogo Type-209 submarines and five Son Won-il Type-214 boats with plans to build four more. South Korea's plans also include the possibility of building additional submarines based on indigenous designs and technologies. South Korea’s submarines are diesel-electric, which means they have limits to how long they can operate submerged. Type-209 submarines can stay submerged for two to three days while the Type-214 is equipped with air-independent propulsion and able to remain underwater for two weeks or more.
An SSN is powered by a nuclear reactor and can remain submerged for long periods of time; their endurance is limited largely by the need to replenish food stocks. Consequently, the dwell time of an SSN allows for extended tracking of North Korean submarines, particularly those that might carry nuclear-armed missiles. Remaining submerged provides extended search time as part of a networked array of sensors including surface ships, helicopters, and aircraft. The nuclear reactor of an SSN also provides a high-density power source to run unmanned systems or sensors that would drain power from the batteries of conventional submarines. It is important to note that South Korean SSNs would only be powered by a nuclear reactor and would not carry nuclear weapons.
North Korea has a large submarine force of over 70 boats and its goal to develop submarine-launched ballistic missiles is a serious concern. However, buying or building SSNs will be a costly and an ill-advised solution to that problem, for several reasons.
One study estimated the cost of an SSN at US$2.5 billion each. To have one submarine on station at all times requires two to three submarines in the fleet, accounting for when boats are undergoing maintenance or transiting to their home port. For South Korea to fully cover the three seas it must patrol – east, west, and south – would require six to nine SSNs at an initial acquisition cost of US$15-23 billion. This cost does not include maintenance, logistics, training, and the construction of hardened facilities to protect these boats. Training and maintaining the expertise of personnel is crucial in order to avoid nuclear accidents.
In August 2017, South Korea announced it would increase defence spending for the coming year by 6.9% to US$38.2 billion. The start-up and on-going costs for SSNs would consume a significant part of the defence budget and could be better spent on other anti-submarine warfare assets such as tracking technologies and surveillance aircraft.
President Moon has also made it clear that he intends to pursue in earnest the return of wartime operational control (OPCON), meaning South Korea would be in the lead rather than the US should war break out. To assume wartime OPCON, South Korea must increase a number of capabilities, particularly in the areas of intelligence, surveillance, and reconnaissance. Moon’s 6.9% budget increase is, in part, an effort to acquire these capabilities to facilitate the transfer. SSNs would deplete the resources South Korea needs to achieve this goal.
In contrast to SSNs, Type-214 submarines cost approximately US$330 million. Seoul could buy five or six of these for the cost of one SSN. Though the SSN is a more advanced platform, the Type-214 is no slouch, and there remains an important advantage of quantity over quality. In addition, diesel-electric submarines run more quietly than an SSN. Given North Korea’s technical limitations, it likely has difficulty tracking either a Type-214 or an SSN, making the less costly option even more viable.
Finally, the most difficult hurdle may come if South Korea seeks to purchase SSNs from the US. Despite President Trump’s announcement in Seoul that 'South Korea will be ordering billions of dollars of equipment', the US has never sold a nuclear-powered submarine or the related technology to anyone. The technology is too valuable and sensitive, even for sharing with allies. If Seoul opts to build its own SSNs, an effort that could take five to six years, this would require changes to a bilateral agreement with Washington that limits South Korea’s ability to enrich uranium and reprocess nuclear fuel for military purposes. It is not clear how willing Washington would be to alter this arrangement.
In the end, acquiring SSNs would provide South Korea with a submarine force with many advanced capabilities, but not enough to justify the cost. Type-214 diesel-electric boats are very capable and can be fielded in greater numbers. Moreover, the money that would be devoted to buying SSNs would be better spent on other defence priorities. In short, for what the South Korean Navy would gain, the cost is not worth it.
I want to thank CDR Joe Santos, US Navy and colleague at the Naval War College for his very helpful comments and input to this article.