South Korea's New Nuclear Submarines

By Jaehyun Lee, Yoonjung Cho

“(…) I have given them approval to build a Nuclear Powered Submarine, rather than the (…) diesel powered Submarines they have now.”

President Donald Trump recently posted on his social media account, and announced that the US has allowed South Korea to build their own nuclear powered submarine. It was revealed right after the recent ROKUS sumit in Gyeongju, South Korea. Owning a nuclear submarine will bring significant changes to the ROK navy’s military capabilities and millitary tension in the East Asian region. What led to this aprupt change of US policies- from dissenting against the ROK’s own nuclear submarine for 30 years to suddenly allowing them?

On Oct. 29, at the ROK-U.S. summit, South Korean President Lee Jae Myung openly asked for President Trump’s authorization of ROK’s construction of nuclear submarines. On the 30th, Trump expressed his approval on his social media platform, on a condition that the construction must take place at Philly Shipyards in the U.S. The Philly shipyards do not have the accomodations for building a nuclear sub. Large investments will be needed to construct the infrastructure needed to build nuclear subs in Philadelphia. Trump is persistent on building the submarines in the U.S., but Korean officals suggest that building the submarines in Korea would be far more reasonable. South Korean company Hanwha’s recent acquisation the Philly shipyards makes the case stronger that the subs should be built in South Korea where there already are working facilities. The shipyards in Philadelphia lack nuclear-related infrastructure, while South Korean shipyards are already equipped with the facilities. If the nuclear submarines are built in the U.S., the project could be delayed well into the 2030s. Discussions on where to build the submarines are still ongoing, and the final decision is yet to be made.

So what exactly are nuclear subs, and how big of an event- that South Korea will operate one at least- is it? There are three types of nuclear submarines: SSN, SSBN, and SSGN. All three refer to submarines that run on nuclear fuel, but an SSBN and SSGN have the capability of firing ballistic missiles and cruise missiles, respectively. An SSN is a nuclear attack submarine; it is the type of submarine South Korea will likely operate in the future.

The main advantage of an SSN comes from the nuclear reactor. Submarines of the South Korean Navy are currently one hundred percent diesel-run. Diesel engines need air to burn its fuel, so diesel subs cannot fully stay underwater. The period for surfacing depends on how fast the submarine is cruising, and how much energy its batteries can store. Nevertheless, diesel subs have to emerge every few days.

There are ‘AIP(air-independent propulsion) submarines,’ which are diesel subs that do not require air to burn fuel. Still, they fall behind nuclear subs on the engine’s operational lifetime. Theoretically, when assumed that food and water are sufficient, nuclear submarines can stay submerged for 15-20 years before having to return to port and replacing its reactor.

Due to its ‘near-permanent’ energy source, SSNs have bigger operation range and higher speed availability. Having at least one gives the operator nation an extreme capability in military-purpose spying. These submarines could stay submerged, undetected, right in front of enemy shores.

As of 2025, only six countries operate nuclear submarines. Below is a chart from Statista, showing the number each nation operates underwater.

These statistics imply that, even when South Korea deploys just one nuclear sub into the ocean, they earn a maritime status only six nations have previously achieved. The South Korean Navy can theoretically spy on every corner of the ocean, undetected. They will become much more competent as a ‘blue-water navy.’

A blue-water navy is a navy capable of exerting their maritime power globally, in open oceans and deep seas. The South Korean Navy(ROKN) has been getting close to being acknowleged as one, by founding its Task Fleet Command back in Feb. 2025 and deploying its newest Aegis destroyer, ROKS Jeongjo the Great, back in Nov. 2024. ‘European Security & Defence,’ a military newspaper, recently stated in an article that operating a nuclear sub ‘continues to provide an unrivalled capacity to undertake long-range, oceanic deployment.’ Given this backdrop, South Korea’s SSN will surely enhance its status as a globally acknowledged maritime power.

Operating a nuclear submarine is clearly an enhancement in military capabilities, but for South Korea, it may not just be an option. Tensions in the region are consistently growing, and as the United States and the People’s Republic of China(PRC) are competing against each other in a power rivalry, strategic competition has become extreme.

On Nov.7 2025, a brand new Chinese aircraft Carrier, the Fujian, started its service in the Chinese Navy. Martime expert Nick Childs, who works at the International Institute for Strategic Studies, stated in an interview by BBC back in Sep. 2025: “The Chinese shipbuilding capacity is something like 200 times overall that of the United States.”

The Chinese Navy is also now the biggest in size; 234 warships against the US Navy’s 219. From a 2024 report by the US Department of Defense, the size of the US Navy has stayed stagnant since the early 2000’s, while that of the Chinese Navy has consistently grown at an incredible pace. Below is a chart that shows the difference.

North Korea is also continuing their missiles tests. On Oct 22 this year, they conducted their first launch in five months, the first under South Korea’s Lee regime. However, on Nov. 7, they conducted another launch after the US raised North Korean sanctions. Back in March 2025, the North Korean News Agency KCNA reported that Kim Jong Un inspected the ‘nuclear-powered strategic guided missile submarine’ under construction. According to Yonhap News Agency, this likely refers to a SSBN of their own. Military threats from neighboring nations will likely continue, and a nuclear submarine may be South Korea’s choice to offset the power imbalance.

Questions about the general feasibility of the project still reamain. Cost, infrastructure, and timeline must be taken into consideration. The requirement to build the subs in U.S. shipyards adds additional procedural steps. Reactions of other countries also suggest that both South Korea and the U.S. should be cautious in making any future steps. U.S. defense Secretary Pete Hegseth expressed full support, while China seems wary of the expansion of South Korea’s nuclear-power capabilities. The country also pointed out that the plan goes against the Nuclear Proliferation Treaty, a treaty signed in 1968 to prohibit utilization of nuclear fuel. Japan is likely to initiate on pursuing the ambition of their own nuclear-powered submarines. Now that South Korea has secured U.S. approval, both governments must settle on a clear and realistic plan in order for the project to deliver a meaningful strategic value.