North Korea Launches New Ballistic Missile Submarine

Key Findings

• North Korea launched a new ballistic missile submarine, the Hero Kim Kun Ok, on September 6, 2023, at the Sinpo South Shipyard with Kim Jong-un in attendance. The “tactical nuclear submarine No. 841” is diesel-powered and assessed to be capable of carrying nuclear-armed missiles.
• Significant modifications to the submarine will allow the submarine to carry North Korea’s larger Pukguksong SLBMs and the smaller modified KN-23 SLBMs. Most notable is a large hump attached aft the sail with ten vertical missile hatches of varying sizes.
• The launch of the Hero Kim Kun Ok heightens speculation that Kim may request the transfer of modern SSB and SLBM technology from Russia.
• The logical next step is a missile launch from the submarine to demonstrate to the world that the vessel is operational. When such a test will take place is unclear.

On September 6, 2023, North Korea launched a “newly built…tactical nuclear submarine No. 841,” named the Hero Kim Kun Ok (김군옥영웅호).¹ The launching ceremony was attended by Kim Jong-un and held at the Sinpo South Shipyard, where the much-anticipated submarine had been under construction inside one of its construction halls for several years. Satellite imagery captured before, during, and after the launching ceremony provides further details on the launch, the unveiled submarine, and changes to the nearby environment, including the movement of the submersible missile test stand barge.

Launching Ceremony

Image of the Sinpo South Shipyard captured at 7:56 a.m. local time shows the new submarine No. 841 Hero Kim Kun Ok berthed at the maintenance and storage pier at the Sinpo South Shipyard, further south of the construction halls where the launching ceremony would take place later in the day. The imagery shows vehicles and personnel along the pier, preparing the submarine for the launching ceremony that will take place later in the day by the construction halls.

Imagery analysis shows changes to other components of the Sinpo South Shipyard as well. The floating dry-dock usually berthed along the maintenance and storage pier was moved to a small boat basin to the southwest of the pier. Notably, the submersible test stand barge and the infiltration mothership that are usually found in the secure boat basin further north have also been moved to this smaller boat basin typically used for fishing vessels. The submersible test stand barge and the infiltration mothership were moved to the smaller boat basin by the maintenance and storage pier sometime between September 2 and September 5. The SINPO-class 8.24 Yongung–which is no longer North Korea’s sole ballistic missile submarine–is slightly visible under the canopy inside the basin.

Later in the day, three vessels, presumably used to help move the newly built submarine from the maintenance and storage pier to the construction halls for the launching ceremony, are observed in the secure boat basin.

Imagery collected later in the day, at 11:20 a.m., shows the new submarine moved to the smaller construction hall and the launching ceremony underway. 

After the launching ceremony by the construction halls at the Sinpo South Shipyard, the submarine was moved back to the maintenance and storage pier further south of the shipyard. The next day, on September 7, 2023, Kim Jong-un visited the pier as the submarine prepared “for a shakedown cruise.”²

Imagery captured on the same day shows the submarine still berthed along the maintenance and storage pier at the Sinpo South Shipyard. The floating dry-dock, submersible test stand barge, and infiltration mothership are still present at the small boat basin to the south of the pier.

Notably, by the next morning on September 8, 2023, the submersible missile test stand barge was moved from the small boat basin to berth right next to the new submarine. While it is too early to determine why the barge was moved to this location, such activity may indicate preparations for testing in the near future.

Hero Kim Kun Ok

North Korea announced that the new ballistic missile submarine is a “tactical nuclear attack submarine,” suggesting that the Hero Kim Kun Ok (Pennant No. 824) is North Korea’s first nuclear-capable submarine.³ However, it should be emphasized that this phrasing is misleading, as the submarine is diesel-powered rather than nuclear. The submarine is believed to be the long-awaited modified ROMEO-class submarine, sometimes called the SINPO-C Class, which was first revealed to the public during Kim Jong-un’s visit to the new construction hall at the Sinpo South Shipyard in July 2019. The reporting in 2019 referred to the modified ROMEO-class submarine as a “newly built submarine,” consistent with today’s reporting of the Hero Kim Kun Ok.

Although it is too early to provide a definitive analysis, initial measurements of the new submarine in satellite imagery indicate that there have been minimal, if any, changes to the overall length of the submarine. This suggests that rather than an expansion of the vessel, substantial changes have occurred inside the submarine, which undoubtedly leads to a reduction of operational capability. Images of the launching ceremony also provide more details of the modifications.

The most notable modification to the submarine is the addition of a large hump attached aft of the sail with ten vertical missile compartments, with four larger and six smaller hatches. As several analysts have suggested, the different sizes of the missile hatches strongly indicate the intent to launch different missile systems using the Hero Kim Kun Ok.⁴ This intent is further supported by North Korea’s missile development over the past four years. At the time of their reveal, the Pukguksong-3, Pukguksong-4ㅅ, Puksuksong-5ㅅ, and the unnamed SLBM revealed in the April 2022 parade were noticed to have been too large in diameter to be launched by North Korea’s then-sole ballistic missile submarine, SINPO-class SSBA.⁵ The larger launch tubes observed on the new submarine Hero Kim Kun Ok suggest that the later Pukguksong models were developed for launching from this new submarine. Additionally, the six smaller missile hatches may be used for the modified KN-23 SLBM, which was first revealed to the public during the Self-Defence-2021 expo on October 12, 2021, and later tested on October 19, 2021, from the SINPO-Class SSBA.⁶ It is too early to determine whether the new submarine has torpedo tubes for launching submarine-launched cruise missiles.

Additional modifications visible in the released images include the reshaping of the bow and the relocation of the diving planes, likely to support the increased mass and provide additional directional stability. Along with these externally visible modifications, the submarine likely has a smaller crew to accommodate the internal modifications.

Shortly after the launching ceremony, the South Korean Joint Chiefs of Staff assessed the submarine as “not in a form to operate normally.”⁷ The submarine, if and when operational, has the potential to significantly increase the launching capabilities of North Korea’s sea-based ballistic missile force and complicate defense by the United States, South Korea, and Japan.

What’s Next?

The logical next step for North Korea is a missile launch from the submarine to demonstrate to the world that the vessel is operational. When such a test will take place is unclear. For example, the SINPO-class ballistic missile submarine was first observed in satellite imagery in July 2014.⁸ The vessel was then used for a test of the Pukguksong-1 (KN-11) on November 28, 2015, approximately a year and half after its initial observation.⁹ Although North Korea claims to have conducted a test of the Pukguksong-1 with the SINPO-class submarine earlier in May 2015, it is widely believed that the May test was a basic at-sea ejection test conducted from a submersible test stand barge.

How North Korea will proceed with its ballistic missile submarine program is unclear at this time. Given that North Korea is known to have 17 to 20 ROMEO-class submarines, one of which has now been modified to become the Hero Kim Kun Ok, it may choose to continue to produce similarly modified submarines, modify the current vessel further by extending it, design an entirely new class of submarine, or a combination of these options. What is clear, however, is that North Korea is continuing to slowly develop its operational ballistic missile capabilities. This effort could be accelerated in Kim’s likely summit with Russian President Vladimir Putin early next week, where the North Korean leader may request the transfer of modern SSB and SLBM technology from Russia.