In 2022, North Korea fired a submarine-launched ballistic missile (SLBM) from a reservoir. At the time, the military authorities failed to detect the SLBM launch in advance and only tracked its trajectory after launch. It was effectively the moment the "Kill Chain" was neutralized.
The Kill Chain refers to military capabilities that detect an enemy's attack and preemptively respond to neutralize it. The time it takes for a missile fired by North Korea to reach Seoul is only 3 to 6 minutes, and as North Korea has advanced its submarine and SLBM technologies, detection has become more difficult, making this the moment when modernization of the Kill Chain is required.
Lee Jae-myung, the president, publicly asked U.S. President Donald Trump at the Korea-U.S. summit on the 29th to "allow the supply of fuel for nuclear-powered submarines," as a step to strengthen the Kill Chain. With Trump approving submarine construction in just one day, the military's program to acquire nuclear-powered submarines appears set to gather momentum. Trump said on his social media, "I have approved Korea to build nuclear-powered submarines."
A nuclear-powered submarine and a nuclear-armed submarine are different concepts. Both use a nuclear-fueled reactor for propulsion, but a nuclear-powered attack submarine (SSN) uses conventional weapons made with gunpowder. In contrast, a nuclear-armed ballistic missile submarine (SSBN) carries nuclear missiles and provides nuclear deterrence.
The government's request to revise nuclear guidelines and build nuclear-powered submarines in return for a tariff negotiation is a measure to defend against North Korea's attempts to neutralize the Kill Chain. North Korean submarines can slip out of base covertly and fire SLBMs in a surprise attack, making prior detection virtually impossible.
A nuclear-powered submarine is needed to quickly detect enemy movements. Because it operates on nuclear fuel, it can conduct underwater operations for extended periods and monitor enemy bases around the clock. The 3,600-ton Jang Yeong-sil, which held a launching ceremony on the 22nd, boasts the most advanced performance among diesel submarines, but due to the nature of diesel fuel, its maximum submergence period is about three weeks.
Experts believe that revising the nuclear agreement would make it possible to build a nuclear-powered submarine within a few years. After the currently ongoing Jangbogo-III Batch-2 submarine program, the government plans to build three additional next-generation submarines through the Jangbogo-III Batch-3 program, and their propulsion can be nuclear. The target for construction is 2029.
There has been no mention of the submarine's nuclear fuel. Trump only said, "Approval has been granted for Korea to build nuclear-powered submarines, and they will be built at a shipyard in Philadelphia, United States."
Industry officials see the possibility that if the United States supplies the material, highly enriched uranium of 80% to 90% used by U.S. nuclear submarines could be used as fuel. Its high energy density allows long-term submarine operations with a small amount of uranium. France and China, among others, use low-enriched uranium under 20% for nuclear-powered submarines due to safety concerns.
Experts also say that, in the long term, the nuclear agreement must be revised to secure technological and construction autonomy for nuclear-powered submarines. Under the Korea-U.S. nuclear agreement revised in June 2015, Korea can reprocess spent nuclear fuel and enrich uranium under 20% only in research fields. Even then, prior U.S. approval is required and only for peaceful use. Military use is prohibited.
Moon Keun-sik, a special professor at Hanyang University's Graduate School of Public Policy, said, "Korea possesses world-class shipbuilding capability and nuclear power technology, so if the nuclear agreement is revised, a nuclear-powered submarine could be secured around 2030," and added, "Because a full revision of the nuclear agreement would take a long time, it should be done by adding an exception clause through an executive order by President Trump."