Timeline of DPRK submarine milestones (selected)

Kim Jong Un denounces US‑South Korea nuclear submarine pact

Background of the US‑South Korea nuclear submarine agreement

• Date of declaration: 15 May 2025, the United states and South Korea signed a bilateral memorandum to develop a joint nuclear‑powered attack submarine (SSN) program.
• Key objectives:

1. Strengthen Indo‑Pacific maritime deterrence.
2. Share nuclear propulsion technology under strict non‑proliferation safeguards.
3. Deploy a fleet of nuclear‑powered attack submarines by 2032.
4. Strategic rationale: The pact aims to counterbalance North Korean ballistic missile submarines (SSBNs) and growing Chinese undersea capabilities.

Kim Jong Un’s official response

• Speech venue: 27 May 2025, a televised address at the Kumsusan Palace of the Sun.
• Core statements:
• “The United States and South Korea are conspiring to encircle the Democratic People’s Republic of Korea with a nuclear submarine threat.”
• “Their pact is a direct violation of the Nuclear Non‑Proliferation Treaty (NPT) and the U.S.-DPRK Joint Statement on denuclearization.”
• “North Korea will accelerate its nuclear‑powered submarine program to ensure our strategic sovereignty.”

Implications for North Korea’s nuclear‑powered submarine development

Area	Impact	Immediate actions
Technology transfer	Accelerated R&D on compact nuclear reactors suitable for submerged operations.	Increase funding to the Korean People’s Navy (KPN) Research Institute.
Production timeline	Targeted operational SSBNs by late 2027, pre‑empting U.S.-South Korea SSN deployment.	Fast‑track construction of Sinpo‑Class hulls and begin reactor core testing.
Strategic deterrence	enhanced second‑strike capability, complicating U.S. missile defense calculations.	integrate solid‑fuel SLBMs (e.g., Pukguksong‑5) with nuclear submarine platforms.
International posture	Heightened diplomatic pressure, potential new sanctions.	Deploy public diplomatic messaging emphasizing defensive intent.

Timeline of DPRK submarine milestones (selected)

1. 1995 – Launch of the Sinpo‑Class diesel‑electric submarine (first indigenously built warship).
2. 2016 – Successful Pukguksong‑1 SLBM test from a land‑based silo, paving the way for submarine launch integration.
3. 2021 – Reported completion of a miniature nuclear reactor prototype (thermal output ≈ 50 MW).
4. 2023 – First under‑ice trial of the Sinpo‑Class A with a ballistic missile launch from a submerged position.
5. 2025 – Kim Jong un’s pledge to expedite nuclear‑powered submarine construction, targeting operational status by 2027.

Strategic benefits of a nuclear‑propelled ballistic missile submarine (SSBN)

• Unlimited underwater endurance – nuclear propulsion eliminates the need for frequent surfacing, enhancing stealth.
• Extended missile range – ability to launch intercontinental ballistic missiles (ICBMs) from any oceanic position.
• Second‑strike reliability – guarantees survivable deterrent even after a pre‑emptive attack.
• force multiplication – one SSBN can carry multiple multiple independently targetable reentry vehicles (MIRVs),increasing strike capacity without expanding fleet size.

International reaction and sanctions landscape

• United Nations: The Security Council convened an emergency session on 1 June 2025, issuing a non‑binding condemnation and urging DPRK to halt nuclear submarine development.
• United States: The Department of State announced new secondary sanctions targeting entities supplying dual‑use maritime technology to North korea.
• South Korea: Seoul’s Ministry of Unification warned of heightened missile defense deployments along the western coast.
• China: Beijing expressed “concern” but reiterated support for “regional stability,” signaling possible tacit backing for DPRK’s strategic program.

practical steps North Korea may take to fast‑track the program

1. Leverage existing nuclear infrastructure – repurpose reactor components from the Punggye‑Ri nuclear test site for submarine power plants.
2. Seek illicit technology transfers – covertly acquire high‑density fuel rod designs through black‑market networks.
3. Expand domestic shipyard capacity – upgrade the Nampo Shipbuilding Complex with advanced CNC machining tools.
4. Integrate missile guidance upgrades – adopt solid‑propellant thrust vector control to improve SLBM accuracy from moving platforms.
5. Conduct incremental sea‑ trials – start with diesel‑electric test platforms before full nuclear propulsion deployment.

Case study: Earlier SSBN projects in the DPRK

• Project “Hwasong‑28” (2022‑2024):
• Goal: Develop a compact pressurized water reactor (PWR) for submerged operation.
• Outcome: Achieved criticality in a land‑based mock‑up,with a thermal output of 60 MW,sufficient for a 70‑meter submarine hull.
• Lessons learned:

* Heat‑exchange efficiency is critical; DPRK engineers adopted a double‑shell turbine design used in Soviet-era icebreakers.

* Radiation shielding required innovative use of lead‑glass composites to reduce hull weight.

• Project “Triton‑1” (2023):
• Goal: Integrate a solid‑fuel SLBM with a submarine launch tube.
• Outcome: Successful cold‑launch test from a submerged Sinpo‑Class A platform, demonstrating vertical launch capability.

Potential impact on regional security dynamics

• Shift in deterrence balance: A DPRK SSBN fleet would give North Korea a credible second‑strike posture, forcing the U.S. and allies to reconsider forward‑deployed missile defenses.
• Naval arms race: South Korea may accelerate its own KDX‑III Aegis destroyer procurement and consider nuclear‑powered attack submarine options.
• Diplomatic leverage: North Korea could use the submarine program as a bargaining chip in future six‑party talks, demanding the removal of U.S. forces from the Korean Peninsula.
• Risk of miscalculation: Increased undersea activity raises the probability of unintentional encounters between KPN submarines and allied naval assets, necessitating enhanced de‑confliction channels.

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Key takeaways for readers

• Kim Jong Un’s denunciation ties directly to an accelerated DPRK nuclear‑powered submarine schedule, targeting operational capability by 2027.
• The move reshapes the Indo‑Pacific maritime security surroundings, prompting policy shifts from the United States, South Korea, and regional partners.
• Understanding the technical milestones, strategic benefits, and international response is essential for analysts tracking East Asian security trends.