South Korea’s Mysterious Submarine-Launched Ballistic Missile Tested From Underwater Platform: Report

Officials remain tight-lipped, but it seems South Korea’s latest submarine could start ballistic missile tests fairly soon.

byThomas Newdick|
South Korea photo


South Korea has apparently joined an elite group of military powers to have successfully developed a practical submarine-launched ballistic missile, or SLBM. Although details remain scarce, local media report that a waterborne test of the missile was successful. Should Seoul now progress to fielding an operational SLBM capability on its submarine fleet, it will notably become the only non-nuclear-armed nation to introduce this type of weapon.

South Korea’s YTN news broadcaster reported the successful underwater launch of an SLBM, citing confirmation from an unnamed military official. What’s not clear is the exact type of missile involved, although it appears to have been launched from a submerged barge, rather than a Republic of Korea Navy (ROKN) submarine. This is standard procedure for initial tests of weapons in this class before they are taken aboard a submarine.

A South Korean Hyunmoo 2 ballistic missile (left) is launched together with an MGM-140 Army Tactical Missile System during a joint South Korean/United States military exercise in 2017., US Army

YTN describes the SLBM involved in the test as a modified Hyunmoo 2B ballistic missile to which it attributes a maximum range of around 300 miles. The SLBM version of this weapon is reportedly known as the K-SLBM or Hyunmoo 4-4.

An earlier, land-based launch of a Republic of Korea Army Hyunmoo 2B ballistic missile:

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This latest reported development follows the launch of an SLBM from a ground test facility at Anheung late last year

According to YTN, the ROKN is due to receive the first of its indigenous Dosan Ahn Changho class conventionally powered submarines later this month and this is expected to be the service’s first vessel capable of carrying SLBMs. Currently, the initial boat is “completing the evaluation of the torpedo decoy launch system,” according to the same source.

“I assume that the Navy is still not in the phase of being able to launch SLBMs from a dived submarine,” another unnamed military official told Yonhap News. “As far as I know, however, technical development to acquire necessary capabilities is ongoing.” That would also seem to point to the fact that the ROKN will gain a submarine-based SLBM capability once the first of these new submarines is commissioned into service, possibly in the next few weeks.

With that in mind, Yonhap further reports that the lead submarine in the Dosan Ahn Changho class could perform a test launch of the new SLBM “imminently.”

The Dosan Ahn Changho class, which was developed under the third phase of the Korean Attack Submarine program, or KSS-III, has provision for six vertical launch system (VLS) cells that will be able to accommodate SLBMs or cruise missiles. Subsequent vessels in the class are expected to increase the capacity to 10 VLS cells.

A model of the Dosan Ahn Changho class submarine., Teukwonjae707/Wikimedia Commons

The Dosan Ahn Changho class is significantly bigger than any previous ROKN submarines, at around 3,000 tons, and is equipped with an advanced lithium-ion battery-based air-independent propulsion system.

Despite a lack of official details, the fact that Seoul has been working on an SLBM program has been known for over five years — you can read our initial reporting on it here. Its development has paralleled studies into the practicality of a future nuclear-powered submarine.

So far, however, there has been no official acknowledgment from Seoul that it intends to field SLBMs on the Dosan Ahn Changho class, although this would seem to be the only realistic option, at least in the short term. 

Moreover, since last month South Korea is permitted to develop ballistic missiles capable of reaching targets far beyond the Korean Peninsula after U.S. President Joe Biden and South Korean President Moon Jae-in agreed to scrap the previous restrictions that had been in place since 1979. Although these guidelines had been updated on several occasions, most recently they limited Seoul to developing missiles with a maximum range of 500 miles.

This change could open the door to South Korea developing SLBMs with a range greater than 500 miles, and certainly in excess of the 300 miles attributed to the Hyunmoo 2B. 

“Without the restrictions on missile ranges, observers believe South Korea is likely to prioritize the development of intermediate-range ballistic missiles with a maximum range of 1,000-5,000 kilometers capable of reaching targets beyond the Korean Peninsula,” Defense News reported last month. “It is also possible Seoul could try developing longer-range submarine-launched ballistic missiles or conduct research on hypersonic weapons.” 

Still, exactly how large a missile these new submarines can hold remains to be understood, but future submarine designs could expand on its vertical launch capabilities.

South Korea’s apparent SLBM ambitions have to be seen in the context of increased tensions with North Korea in recent years, as well as that country’s own submarine-launched ballistic missile developments. Of course, outside of its still-mysterious SLBM program, Pyongyang is also highly active in the development of various land-based nuclear weapons and delivery systems.

An extended-range SLBM, of the type that would now be permitted with the demise of the previous restrictions, would also provide South Korea with a means of deterring potential enemies further afield, such as China and Russia.

What is likely to be North Korea’s first operational nuclear-armed submarine seen under construction during one of Kim’s inspections., NK State Media

Above all, though, there is the question of how South Korea would really benefit from an SLBM capability. The ROKN already has its submarine-launched cruise missiles, providing another survivable means of delivering a conventional warhead. And, should a conflict with the north escalate to a nuclear exchange, South Korea supposedly receives protection from America’s nuclear umbrella.

While the status of Seoul’s nuclear-powered submarine program is currently unclear, a conventionally powered design like the Dosan Ahn Changho class once provided with SLBMs, would provide something akin to a second-strike capability, albeit conventional, to help to deter an attack from the north. During a conflict, South Korea sees its increasingly capable ballistic missile arsenal as essential to hitting critical targets throughout the north, and the kinetic energy provided by a ballistic missile allows for far greater penetration against bunkers and critical regime targets than cruise missiles or most direct attack weapons. They are also far harder to defend against. You can read all about this strategy here

A Republic of Korea Navy test of a domestically designed submarine-launched land-attack cruise missile:

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Then there is the prospect that, ultimately, Seoul is eyeing a nuclear payload for its emerging SLBMs. It’s possible that South Korea views an independent nuclear deterrent as the ultimate safeguard against North Korean aggression but, again, there is no official word on this. However, an argument could be made that an advanced submarine armed with nuclear-tipped SLBMs would be one way of warding off the threat from the north without the need to rely on the United States. This all comes as North Korea looks set to deploy its first nuclear-armed submarine in the not too distant future. 

It remains to be seen just how South Korea will continue with its SLBM program, when we might see these weapons deployed, and if there are longer-term plans for increased-range missiles and even nuclear warheads. It could be the case that Seoul is pursuing an SLBM onto which a nuclear warhead could be added as an insurance option of sorts, should North Korea dramatically expand its own undersea nuclear arsenal and/or if the geopolitical winds change between it and its long-time national security partner, the United States. As it is, a conventional SLBM offers only limited deterrence value and doesn’t significantly alter the strategic balance in the region.

For now, however, reports of this successful underwater missile test suggest that the country has joined the select group of nations able to design and successfully test its own SLBMs. Bearing in mind the difficulties in mastering these technologies, this is a significant achievement in itself.

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