Are South Korean Submarines About to Go Nuclear?

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March 9, 2019 Topic: Security Region: Asia Blog Brand: The Buzz Tags: MilitaryTechnologyWeaponsWarSouth KoreaSubmarine

Are South Korean Submarines About to Go Nuclear?

There may soon be two nuclear powers on the Korean Peninsula.


Since his election in 2017, South Korean president Moon Jae-in has transformed his country’s diplomatic posture towards North Korea from one of confrontation to almost aggressive engagement.

However, that didn’t prevent Moon from attending the launch ceremony on September 14, 2018, of large new missile submarine from a shipyard on Geoje island, near Pusan.


“Our path to peace will not end when accompanied by a strong military and strong defense,” he remarked.

The new vessel, designed to unleash cruise and ballistic missiles on land targets and hunt down North Korea’s own missile submarines, is the first of nine planned KSS-III submarines to be built by domestic firms Daewoo and Hyundai at a cost of $700 million to $1 billion each.

The lead ship Dosahn Ahn Chango is named after a legendary Korean independence activist. This is fitting because South Korea’s ambitious plans for the class may lay the groundwork for strategic capabilities increasing Seoul’s independence from its historic alliance with Washington.

The KSS-III is South Korea’s first domestically-designed submarine and embodies the third phase of South Korea’s attack submarine program begun in the 1990s. For the first two phases, South Korea imported or license-built nine improved variants of the German Type 209 submarine (the Chang Bogo-class), followed by nine more advanced Type 214 submarines (Son Won-il-class).

Like the Type 214 and the Type 218 Invincible recently launched by Singapore, the KSS-III has an advanced hydrogen fuel-cell air-independent propulsion system. Traditional diesel-electric submarines must periodically surface or snorkel to run their air-breathing diesel-engines to recharge batteries—exposing themselves to detection and attack. However, an AIP submarine can generate enough electricity while underwater to sustainably cruise at slow speeds (around five knots) for weeks—though it can still briefly surge to 20 knots in emergencies.

Fuel-cell AIP is quieter and more efficient than the Stirling heat-cycle AIP systems used on Japanese and Chinese submarines. Moreover, the KSS-III’s configuration reportedly has 20 percent greater endurance. Given the proximity of South Korea’s potential adversaries, the submarine’s fifty-day endurance and reported ten thousand nautical mile range is more than adequate.

Seventy-six percent of the KSS-III is reportedly built with domestic components, including the vessel’s Naval Shield combat system integrating sensors and controls for the crew, and its multiple sonars. The sub’s ultra-quiet indigenously-designed, seven-bladed skewback propeller remains censored in official photos.

However, the KSS-III does incorporate foreign hardware, including the quiet pressurized torpedo loading and launch system used in the British Royal Navy’s Astute-class submarines. The KSS-III’s Spanish Pegaso electromagnetic sensor (ESM) allows it to discreetly detect and identify the emissions of opposing sub-hunters, and it can also spy on nearby vessels using a French-designed non-penetrating optronic mast—functionally a stealthy hi-tech periscope loaded with electro-optical sensors.

The 83-meter long KSS-III displaces more than twice as much as South Korea’s other subs at 3,700 tons submerged. The crew of 50 reportedly benefits from individual beds instead of having to share ‘hot bunks’, and enlarged food stores to sustain long-range patrols.

However, the vessel’s bulk is primarily due to the six Korean-designed vertical launch systems (VLS) on its spine—making her the only VLS-equipped diesel-electric submarine in service save for a lone Chinese test-bed submarine. While other subs can launch missiles from their torpedo tubes, a VLS allow for rapid ‘ripple-firing’ more likely to overwhelm an enemy.

Currently, the Dosahn Ahn-Chang’s cells can carry surface-skimming Hyunmoo-3C land-attack cruise missiles with 1,100-pound warheads. Guided by inertial navigation, GPS and a terrain-imaging system, these can strike targets up to 930 miles away—meaning they could hit anywhere in North Korea and well beyond.

However, in 2016 South Korean military officials announced the KSS-III would also be capable of launching submarine-launched ballistic missiles (SLBMS), which arc high up towards space before plunging down towards their targets at greater speeds.

This may have been spurred by a perceived need to “match” North Korea’s development of the Sinpo submarine, which can launch Pukkuksong-1 nuclear-tipped SLBMs from underwater.

The KSS-III will likely incorporate a derivative of the land-based Hyunmoo-2B or C ballistic missiles, which have a range of 500 miles carrying warheads between 1,000-2,200 pounds. These could fired underwater using a ‘cold launch’ system reportedly derived from the Russian S-400 surface-to-air missile system. Unconfirmed reports claim South Korea has already successfully tested the underwater launch system.

South Korea’s motives for pursuing SLBMs are unclear. Ballistic missiles are more difficult to intercept than cruise missiles and potentially better for busting hardened command bunkers or nuclear weapons sites, but greater expense and lower precision has traditionally relegated SLBMs to delivering nuclear-warheads. For example, a Hyunmoo-2B lands within 30 meters of its target half the time.

As nuclear ballistic missile armed submarines are the gold-standard of unstoppable nuclear deterrence, Seoul may be quietly laying the foundations for deploying its own sea-based nuclear deterrence.

South Korea makes extensive use of civilian nuclear power and could develop its own nuclear weapons rapidly should it decide to. Historically, though, pressure and inducements from the United States have prevented Seoul from pressing forward. Limiting the number of actors with nuclear weapons is desirable to Washington as it makes nuclear escalation easier to control.

As a result, North Korea has placed more emphasis on negotiations with the U.S. than Seoul due to the former’s nuclear weapons. A South Korea committed to long-term co-existence with a nuclear-capable North Korea may eventually seek its own capability to counter-balance Pyongyang’s leverage.

South Korea may also transform the Hyunmoo-2 into a potent anti-ship weapon by installing a multi-mode seeker.

After the third KSS-III submarine is launched by 2024, South Korea plans a bigger and better Batch 2 trio with displacement rising above 4,000 tons as the hull is lengthened ten meters to increase the number of vertical launch systems to ten or twelve.

The Batch 2 boats’ lead-acid batteries will be replaced with a scaled-up version of the lightweight Samsung lithium-ion batteries used in smart phones and laptops. These reportedly recharge ten times faster and can store equivalent energy in one-fourth the volume and at one-fifth the weight, doubling underwater endurance.

Japan deployed the first large operational LIB submarine in 2018. Besides greater cost, deployment of LIB technology has taken time because LIBs are prone to combusting when overheated—a problem which notoriously afflicted batteries in Samsung’s S7 tablets. Thus, submarines LIBs must be hardened and tested to withstand exposure seawater and other adverse circumstances.

Unlike the Japanese Soryu-class, the KSS-III would still retain its fuel-cell system. The combination of sustainable AIP with long-enduring and fast-recharging batteries should not only increase endurance, but may afford it higher sustained cruising speeds.

South Korea plans additional upgrade for the final trio of Batch 3 submarines, to be launched by 2029, but these remain unpublicized. One possibility is an electrically-turned propeller.

Another avenue being quietly explored is nuclear propulsion—a goal within South Korea’s technical capabilities, but fraught with potential violation of Korean de-nuclearization treaties, which ban necessary enriched nuclear fuels. South Korea is reportedly investigating its legal options, and has contemplated pursuing a 65-megawatt light water reactor 7x3.5 meters in diameters, derived from Russian technology.

Nuclear reactors give a submarine virtually unlimited underwater endurance, though this may be of less benefit to South Korea due to its proximity to potential adversaries. It also enables higher sustained cruising speeds of 30 knots, allowing a submarine to outmaneuver, outrun or overtake other nuclear-powered submarines, such as those operated by China.

In time, the extent of South Korea’s ambitious plans for the KSS-III and its submarine-launched missiles may become clearer. For now, the Dosahn Ahn Chang is undergoing sea trials and will begin operational service early in 2022.

Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring.

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