N Korea's Nuclear Sub Engulfed In A Sea Of Doubt

In line with its first line of effort, North Korea unveiled the Hero Kim Kun Ok“tactical nuclear submarine” in September 2023. According to Beyond Parallel, it is a refurbished Soviet Romeo-class conventional ballistic missile submarine (SSB).

Beyond Parallel says the submarine's unveiling aligns with North Korea's SLBM program, with its newer Pukguksong-3, Pukguksong-4, Pukguksong-5 and an unnamed SLBM unveiled in April 2022 too big to fit its current Gorae-class SSB.

According to the Nuclear Threat Initiative (NTI) , as of August 2024, North Korea had one Gorae-class SSB. NTI notes that the submarine is limited by its reliance on diesel engines and lack of air-independent propulsion (AIP) systems. Its range is capped at 2,778 kilometers-sufficient to hold targets in South Korea and Japan at risk but insufficient to threaten the US mainland.

However, Min says that remodeling Soviet-era submarines, as in the Hero Kim Kun Ok and Gorae-class SSBs' case, could introduce structural and engineering problems, which could take significant time and resources to correct, rendering these efforts impractical for North Korea.

Further, in a 2017 article in the Strategy journal, Oh Soon-Kun mentions that North Korea's Gorae SSBs will face significant command and control challenges and combat service support as they operate further from their home bases. Oh also says that the Gorae SSB, a variant of the Soviet Golf-class SSB, has high noise levels, making it vulnerable to anti-submarine warfare (ASW) operations.

Given those limitations, Oh says North Korea could limit its SSBs to operations close to its shore bases, following a Soviet-style bastion strategy. However, he mentions that the approach limits their deterrent value by precluding forward operations.

Alternatively, he states that North Korea could attempt to infiltrate its SSBs into the Sea of Japan, risking detection and destruction by South Korea, the US, and Japan's ASW capabilities.

As for North Korea's second line of effort, Thomas Newdick mentions in an October 2024 article for The War Zone (TWZ) that nuclear propulsion would give North Korea a credible second-strike capability, ensuring unlimited underwater endurance and possibly reduced acoustic signature.

However, Newdick points out that North Korea's ability to build a nuclear-powered submarine is questionable. He notes that building submarine reactors is challenging to master, given their demanding integration and power generation requirements.

Despite those challenges, in an October 2024 Heritage Foundation report , Robert Peters mentions that North Korea has been seeking nuclear submarine propulsion technology for over a decade, with US officials speculating that Russia may have provided North Korea with such in exchange for supporting its Ukraine war effort with soldiers and materiel.

While Alex Luck notes in TWZ that a North Korean nuclear-powered submarine is not an unexpected development, the technical challenges of building such a submarine are daunting.

Luck says North Korea hasn't developed a suitable reactor design, but it may focus on building“hybrid” submarines, combining nuclear and conventional propulsion, as seen in the sole 1980s Project 651E Juliett-class cruise missile submarine (SSG) .

Including a small auxiliary nuclear reactor in its Romeo and Golf-class retrofits could help North Korea simultaneously achieve its two lines of effort in building an underwater nuclear deterrent. A small auxiliary nuclear reactor could offset the range limitations of North Korea's Hero Kim Kun Ok and Gorae-class SSBs and increase their submerged endurance.

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However, taking Project 651E as a precedent, this approach was less than successful, achieving only a sustained speed of six knots underwater for 11,200 kilometers. This poor performance made chemical-based AIP technology, such as fuel cells and lithium-ion batteries, more practical. The Project 651E reactor was disposed of in 2005.

Sukjoon Yoon mentions in an October 2023 article for the S Rajaratnam School of International Studies (RSIS) in Singapore that North Korea's submarine force will likely depend on quantity over quality to match US and South Korean forces.

According to the US Defense Intelligence Agency's (DIA) 2021 North Korea Military Power report , North Korea has about 70 conventional submarines, but they are of older design and limited endurance.

Yoon argues that since North Korea's nuclear submarine projects seem half-baked, the best response for South Korea is to put diplomatic pressure on the former and Russia. However, he says that South Korea's popular media prefers a military response, noting that the country has already built the sophisticated KSS-III SSB , which could have nuclear propulsion.

Yoon mentions that South Korea's KSS-III submarines could perform an“anti-exit” strategy against North Korea's SSBs, preventing them from leaving their bases and going out to sea. However, he says that South Korea constructing a nuclear-powered submarine is still a big request for the US.

Cautioning about North Korea's submarine developments, Yoon says that while the country's efforts may be odd and flawed, the Kim regime's determination to acquire weapons that can threaten South Korea, Japan and the US should not be underestimated and should be addressed urgently.

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