Hey, Boomer: What Happened to North Korea’s Ballistic Missile Subs?

Submarine-launched ballistic missile from an undisclosed location on March 12, 2023 (Image: Korean Central News Agency).

In July 2019, North Korea revealed a conventionally powered ballistic missile submarine (SSB) in the late stages of construction and announced that it would be deployed in the near future. However, since then, there has been no evidence of the SSB’s launch, despite numerous occasions when that was expected. It is unclear what is holding up this process, although there are likely three key factors at play.

  1. SSB efforts are much lower in priority than the North’s land-mobile missiles.
  2. The submarine-launched ballistic missile (SLBM) program is in flux, with three increasingly larger missiles having been unveiled since July 2019, but not yet flight tested—one of which may be too big for the new SSB to carry.
  3. Problems may have been encountered in the construction of the new SSB that Pyongyang has still not overcome, or that may not be cost-effective to rectify, or the SSB may no longer meet the North’s operational needs.

It remains to be seen when or if the new SSB ever sees the light of day. It is possible that the sub will be reconfigured once a suitably sized SLBM completes development or that it will be reconfigured for use in another role, such as supporting minisubs or special operational forces. Pyongyang may decide to dismantle the new SSB altogether in favor of building a larger sub. The SSB may just be left in the construction hall until a course of action is decided or even indefinitely.

Whatever happens with the new SSB, a several-boat SSB force that could truly serve as a consequential and credible “leg” of a nuclear dyad or triad does not seem to be in the cards anytime soon. Pyongyang’s land-based missiles, which are much more survivable and cost-effective than an SSB force, are highly likely to remain the mainstay of its nuclear and missile forces.

A Long Time Coming

In July 2019, North Korean media reported that Kim Jong Un had “inspected a newly built submarine” and that the sub’s “operational deployment is near at hand.” Associated photos showed the presence of what appeared to be a substantially externally complete SSB inside a covered construction hall at the Sinpho South Shipyard. The sub seemed to be based on North Korea’s ROMEO-class submarine, which uses old Soviet technology, and apparently had room for three missile launch tubes in the sail.

North Korea began work on the infrastructure to build a new type of submarine in June 2014, according to analysis of commercial imagery, and by September 2016, construction of the SSB appeared to be underway.

Since mid-2019, there have been several instances where experts and analysts have predicted the imminent rollout of the new SSB based on various shipyard activities, upcoming North Korean ceremonial days, or trends in the North’s missile activities. These include:

  • In September 2019, based on the erection of a concealment structure at the shipyard.
  • In October 2019, based on the first flight test of the Pukguksong-3 (PKS-3) SLBM from a submersible test platform.
  • In December 2019, given “growing speculation concerning a North Korean end-of-year ‘surprise.’”
  • In May 2020, given speculation, triggered by Pyongyang’s touting of “new policies for further increasing the nuclear war deterrence,” that an SSB rollout would be “the most probable step North Korea may take” to make good on December 2019 warnings of a “new strategic weapon.”
  • In October 2020, based on the belief by some of an “increasing” probability of an SSB rollout, reinforced by the upcoming October 10 Korean Workers’ Party Foundation Day celebration.
  • In March 2021, based on the opportunity presented by the end of the North’s annual winter training cycle or presented by the upcoming July-September summer cycle.
  • In April 2021, based on repositioning of the SLBM submersible test barge at the Sinpho South Shipyard.
  • Also in April, based on “mounting speculation” of an SSB rollout given the additional impetus of the impending celebration of Kim Il Sung’s birthday.
  • Yet again in April 2021, based on the imminence of the mid-month “Day of the Sun” anniversary, used in the past for tests of missile technology.
  • In September 2021, based on the “considerable pressure” that was “likely” placed on North Korea to roll out the SSB by “South Korean reports during the past month describing their development and launching of a new class of ballistic missile submarine and reported testing of a submarine-launched ballistic missile.”
  • In May 2022, based on the “increasing probability” of an SSB rollout, “considering the North’s accelerated testing rate of various ballistic missile systems during the past seven months.”
  • Most recently, in October 2022, based on an atypical level of activity at the shipyard.

North Korea could have rolled the SSB out of the construction hall at any time since at least the summer of 2020, when the parts yard apparently used to stage components flowing into the construction hall has been empty, suggesting the end of major construction, or July 2021, when the South Korean press claimed the Republic of Korea (ROK) and US intelligence assessed construction of the SSB was complete. As of June 10, 2023, there was still no open source evidence the SSB has been launched, although it is and will remain the case that the sub could be rolled out at any time in the future.

What’s Taking So Long?

The long period of time since Pyongyang publically reported the SSB’s “operational deployment is near at hand” strongly suggests there are some compelling reasons why the sub has remained in the construction hall.[1] Based on analysis of the available information, one or more of the following three key factors probably explains why the new SSB has been a no-show for almost four years.

Missile subs are not a high priority. When the new SSB was revealed, the US media often claimed that Kim Jong Un was “determined to deploy it as soon as he can” and had a “full steam ahead program to perfect his submarines.” Such commentary was bolstered by assessments that North Korea was seeking to develop a “second leg of the nuclear triad,” even “undeniably” so.

Clearly, the SSB program has not actually proceeded in this fashion and has not taken any central role in North Korea’s nuclear force. Pyongyang thus does not appear to have put much priority on ballistic missile submarines, and so there seems to be little pressure to finalize the new sub. (This lack of priority also is reflected in the associated SLBM program, discussed below.) A contrary example of what the North can do when it decides to ramp up the priority of a program is the recent attempt to place a reconnaissance satellite into orbit: a new satellite and space-launch vehicle—the Chollima-1—were developed, and in just over a month a new launch pad was erected from scratch and used to conduct the first (albeit unsuccessful) launch on May 31, 2023.

There are good operational and cost-effective reasons for the SSB not being a priority for North Korea, although we do not know the extent to which those reasons have influenced its decisions. The North’s large, longstanding force of road-mobile, land-based ballistic missiles offers substantially more survivability than noisy ROMEO-based SSBs that would be at substantial risk of acoustic detection and operate under conditions of allied air and naval superiority. SSBs will not expand the target coverage of land-mobile missiles or add meaningfully to the number of warheads North Korea can deliver—which can be done more cost-effectively by adding more truck- or railcar-based land-mobile missile launchers than by adding more resource-intensive, slow-to-build SSBs that only carry three SLBMs each.

The SLBM program is in flux. When the SSB was first unveiled, it was widely assumed that the sub would carry the Pukguksong-3 SLBM (about 8 meters long and 1.6 meters in diameter), a missile revealed by the North in 2017 and flight tested for the first and only time in October 2019. Since then, the North has displayed—but has not yet flight tested—three progressively larger (and thus longer-ranged) SLBMs:

  • The Pukguksong-4 (about 2 meters longer than the PKS-3 and about 2.05 meters in diameter), paraded in October 2020;
  • The Pukguksong-5 (about 1.7 meters longer than the PKS-4, but the same diameter), paraded in January 2021; and
  • A new large SLBM (presumably Pukguksong-6, about 1.6 meters longer than the PKS-5 and about 2.21 meters in diameter), paraded in April 2022.

This lack of SLBM developmental flight testing also suggests lower priority for SSBs. In stark contrast, North Korea has flight tested six new types of land-based ballistic missiles since the only Pukguksong-3 SLBM test in October 2019: two short-range ballistic missiles (SRBMs), two “hypersonic” medium-range ballistic missiles, and two intercontinental ballistic missiles. It also tested two new types of land-attack cruise missiles (LACM).

Having the longest-ranged SLBMs possible makes the most military and operational sense for Pyongyang. This allows the associated missile sub to strike targets that are farther away while staying in waters closer to North Korea (and thus farther from allied anti-submarine assets, and closer to North Korean air and naval assets that can help protect the SSB). The delays in flight testing any of the new SLBMs (reinforced by the lack of any known ejection testing[2]) may well have contributed to the delay in rolling out the new SSB, which would need to have its sail section modified to accept progressively larger launch tubes for the series of new SLBMs.

Moreover, if the new large SLBM is now the missile of choice, it is possible that the new SSB is simply too small to accommodate that missile. This might mean that the SSB has become obsolete even before seeing the light of day.

Further confusing the picture, North Korea launched a KN-23 SRBM from its single-tube GORAE (or SINPO)-class ballistic missile test submarine in October 2021. The test sub apparently is still configured to launch that much smaller, shorter-range missile (about 7.5 meters long and 0.9 meters in diameter) and would need to be reconfigured if it was going to be used in the flight testing of one of the larger SLBMs for ultimate deployment on the new SSB. Moreover, the GORAE’s missile hatch appears to be only 1.8 meters in diameter, which is too small to accommodate the new large SLBM. In any case, a deployed sub-launched KN-23 makes very little military sense, given the North’s large existing force of more survivable land-based SRBMs.

The SSB itself has problems. It is possible that the North encountered problems in the construction of the new SSB (or its conversion from a preexisting ROMEO) that it has still not overcome, that any such problems were somehow insurmountable or not cost-effective to rectify, or that the North came to realize the SSB would not meet its operational needs.[3] An example of the latter reason could be that, as noted above, the sub may be too small to accommodate the new large SLBM.

All that can be said at this point is that there has been no evidence that the SSB has been moved from the construction hall, and given the lack of activity in the construction hall’s parts yard since the summer of 2020, it does not appear that the SSB has thus far been dismantled or subjected to major reconstruction, or that a replacement submarine is being built alongside it.

Future Prospects Uncertain

It remains to be seen when or if the new SSB will ever be launched. There are four main possibilities for its future, listed in descending order of likelihood:

  • North Korea may decide to configure it for a suitably sized missile, such as the KN-23 SRBM; the Pukguksong-3, -4, or -5 SLBMs if any of them complete development; or even a vertically launched version of the “Hwasal” LACM.[4]
  • It may decide to reconfigure the sub for use in another role, such as supporting minisubs or special operations forces—or even the “Haeil” nuclear-armed unmanned underwater vehicle (UUV) if that system truly is intended for deployment.
  • It may decide to dismantle the SSB, perhaps in favor of a larger sub able to carry the new large SLBM. Although likely aspirational in the near term, Kim Jong Un, in his January 2021 report to the Eighth Party Congress, set a task to “possess a nuclear-powered submarine.”
  • Or it may allow the sub to lie fallow in the construction hall, either for another several years until it decides upon one of the above courses of action, or perhaps even indefinitely.

Whatever happens with the new SSB, a several-boat SSB force that could truly serve as a consequential and credible “leg” of a nuclear dyad or triad does not appear to be in the cards anytime soon. Pyongyang’s land-based missiles, which are much more survivable and cost-effective than an SSB force, are highly likely to remain the mainstay of its nuclear and missile forces.

  1. [1]

    It should be noted, however, that true “operational deployment” probably would take a year or more after rollout due to the highly likely need for fitting-out, acceptance trials, commissioning, and shake-down cruises as with other North Korean submarines. See Joseph Bermudez and Victor Cha, “Sinpo South Shipyard: Construction of a New Ballistic Missile Submarine?,” Beyond Parallel, August 28, 2019, https://beyondparallel.csis.org/sinpo-south-shipyard-construction-of-a-new-ballistic-missile-submarine.

  2. [2]

    Before conducting flight tests, SLBM programs usually conduct “ejection tests” or “pop-up tests,” in which the system used to eject the missile from the submerged submarine prior to ignition is tested using a dummy missile and a land-based rig or submersible platform.

  3. [3]

    See Tianran Xu, “Constraints and Outlook: Future Deployment of DPRK Ballistic Missile Submarines,” Open Nuclear Network, January 5, 2022, https://opennuclear.org/publication/constraints-and-outlook-future-deployment-dprk-ballistic-missile-submarines; and Joseph S. Bermudez Jr., Victor Cha, and Jennifer Jun, “Sinpo South Shipyard Update: Vessel Movements and New Construction,” Beyond Parallel, September 15, 2022, https://beyondparallel.csis.org/sinpo-south-shipyard-update-vessel-movements-and-new-construction.

  4. [4]

    See Vann H. Van Diepen, “Initial Analysis of North Korea’s “New Type Long-Range Cruise Missile,” 38 North, September 15, 2021, https://www.38north.org/2021/09/initial-analysis-of-north-koreas-new-type-long-range-cruise-missile; and Vann H. Van Diepen, “North Korea Launches Four “Hwasal-2” LACMs to Show Strong Deterrence and Rapid Response,” 38 North, March 1, 2023, https://www.38north.org/2023/03/north-korea-launches-four-hwasal-2-lacms-to-show-strong-deterrence-and-rapid-response.

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