At the recent APEC Summit, the meeting between South Korea and the United States drew significant attention.
The biggest headline was the news that the U.S. had approved South Korea’s plan to build nuclear-powered submarines.
This decision goes far beyond the addition of a new weapon system — it marks a major step toward strengthening South Korea’s security sovereignty and could have a profound impact on the security landscape of Northeast Asia.
Let’s take a closer look at what this approval means and the key issues surrounding it.
1. Understanding the Nuclear-Powered Submarine (SSN)
The term ‘nuclear submarine’ usually causes confusion. It’s crucial to distinguish between two types:
- Nuclear-Powered Attack Submarine (SSN): The type South Korea is pursuing. It is conventionally armed but uses a nuclear reactor for propulsion (engine).
- Ballistic Missile Nuclear Submarine (SSBN): This type is armed with nuclear weapons (ballistic missiles).
South Korea is focused on acquiring SSNs, which are strategic assets due to their overwhelming performance advantages over conventional vessels.
⚓ The Critical Difference: Unlimited Underwater Endurance
| Feature | Nuclear-Powered Submarine (SSN) | Conventional (Diesel-Electric) Submarine (SSK) |
|---|---|---|
| Power Source | Nuclear Reactor (Fission Energy) | Diesel Engine & Batteries (often with AIP) |
| Submergence | Virtually unlimited (limited only by food/crew endurance) | Limited (must “snorkel” or surface periodically for air/recharge, max. about 3 weeks with AIP) |
| Speed | Sustained high speed (approx. 20+ knots) | Slow speed when submerged on batteries; high speed severely drains power |
| Strategic Value | Unrivaled stealth, rapid deployment, and long-range missions. Essential for deep-sea operations. | Excellent for coastal defense and limited-range missions; vulnerable during surfacing. |
👉 Key Takeaway: The SSN’s ability to stay underwater almost indefinitely and pursue fast targets makes it the ultimate countermeasure for tracking and deterring threats like North Korea’s Submarine-Launched Ballistic Missiles (SLBMs).
2. The Nuclear Hurdle: Why US Approval Was Necessary
Despite being a global leader in nuclear energy technology, South Korea cannot independently produce the enriched uranium required for its submarines. This is due to international non-proliferation agreements and a key bilateral treaty.
📜 The US-ROK Atomic Energy Agreement & NPT
- Nuclear Non-Proliferation Treaty (NPT): As a non-nuclear-weapon state (NNWS), South Korea’s military nuclear activities are heavily scrutinized. While SSNs are not a technical violation of the NPT, their military reactor operation requires special arrangements with the International Atomic Energy Agency (IAEA).
- US-ROK Atomic Energy Agreement (Revised 2015): This agreement requires South Korea to obtain prior consent from the US government for uranium enrichment or reprocessing, even for peaceful purposes.
💡 High-Enriched vs. Low-Enriched Fuel
The debate centers on the fuel’s quality:
| Fuel Type | Enrichment Level | Operational Efficiency |
|---|---|---|
| High-Enriched Uranium (HEU) | \approx 90\% | Ideal for subs: smaller reactor, less frequent refueling (30+ years). Used by US SSNs. |
| Low-Enriched Uranium (LEU) | < 20\% | Lower power density: requires a larger reactor and more frequent refueling. The limit typically allowed for NNWS. |
👉 The Problem: The US decision essentially opens the door for South Korea to secure the necessary nuclear fuel supply or technology, likely through a special waiver or revision of the existing agreement, making the SSN project viable.
3. Analyzing the Mutual Benefits: Why the US Agreed
The US approval is a strategic move, offering substantial gains for both allies.
| Nation | Strategic Benefit |
|---|---|
| South Korea | Enhanced Deterrence: Superior capability to track North Korean SLBMs and respond to sub-surface threats. Increased Security Sovereignty and global military standing. |
| United States | Burden Sharing & Regional Stability: Allows a key ally to acquire advanced capabilities, thus reinforcing deterrence against China’s growing naval power in the Indo-Pacific. Promotes alliance integration. |
🏭 The ‘Philly Shipyard’ Factor
US President Donald Trump stated that the submarine would be built at the Philadelphia Shipyard. This links the defense cooperation to economic benefits, leveraging the multibillion-dollar investment by South Korea’s Hanwha Group in the shipyard (Source: The Diplomat, Korea Herald).
- The ROK Government’s Position: South Korean officials maintain that the hull and reactor would be domestically built in South Korea, with the US primarily supplying the fuel (Source: Korea Herald).
- The Next Challenge: This difference of opinion highlights a major upcoming negotiation: the exact location, technology transfer, and construction model (domestic vs. joint/parallel construction).
4. South Korea’s Manufacturing Capability
Is South Korea actually capable of building an SSN? The answer is generally Yes, with a few key caveats related to nuclear components.
- World-Class Shipbuilding: South Korea has a 30-year history of successfully building submarines, from the Jangbogo-class (KSS-I) to the advanced, domestically designed Dosan Ahn Changho-class (KSS-III), which is equipped with Vertical Launching System (VLS) tubes for SLBMs. (Source: NTI, ROK Navy).
- Nuclear Reactor Expertise: South Korea is a leader in Small Modular Reactor (SMR) technology, such as the SMART reactor. This civilian expertise provides a strong foundation for developing the miniaturized, low-noise reactor required for a submarine.
👉 Timeline: South Korea’s Defense Minister has stated that the country possesses the necessary technology and could achieve operational capability within a decade, aiming for the early 2030s (Source: Asia News Network).
5. Which countries currently possess nuclear-powered submarines?
According to the International Institute for Strategic Studies (IISS), very few countries operate nuclear-powered submarines — the United States has the most with around 66, followed by Russia with about 30, and China with approximately 12.
6. Regional Impact and Remaining Hurdles
🌐 Impact on Northeast Asia
If successful, South Korea would become the eighth country in the world to operate nuclear-powered submarines, joining the US, Russia, China, UK, France, India, and potentially Australia (AUKUS).
While this significantly bolsters deterrence against North Korea, it will likely exacerbate regional tensions and fuel military modernization in neighboring countries like China and Japan, potentially leading to a new phase of the arms race in East Asia.
🛑 Key Remaining Challenges
- Revising the US-ROK Atomic Agreement: A formal revision or a special supplementary agreement is essential to secure the long-term, stable supply of nuclear fuel.
- US Congressional Approval: The President’s approval is a political signal; the process requires navigating the complex US domestic legal framework, including Congressional sign-off on nuclear cooperation agreements.
- Finalizing the Construction Plan: The crucial ‘where’ and ‘how’ (domestic versus joint construction and the level of US technology transfer) must be finalized through difficult follow-up negotiations.
The US approval is a diplomatic milestone and a massive step toward securing South Korea’s future maritime security. However, the true test lies in the upcoming technical and political negotiations required to turn this approval into a tangible vessel.
7. In conclusion…
The outcome of this Korea–U.S. summit can be seen as a landmark decision in the history of South Korea’s national security.
Building nuclear-powered submarines is not just about “developing weapons”; it carries a symbolic meaning that South Korea now has the capability to defend its own waters.
It will be important to watch how this project unfolds amid various technological and diplomatic challenges.
One thing is clear: South Korea’s seas have become significantly stronger. 🌊