S. Korea’s Possession of Nuclear Submarines: Nuclear Nonproliferation, Enhancing Deterrence are Key Aspects

Editorial

16:08 JST, November 6, 2025

Should South Korea possess nuclear submarines with U.S. support, East Asia’s security environment could undergo drastic change. This would also influence the debate on Japan’s possession of its own nuclear submarines. It is necessary to pay close attention to Seoul’s actions on the matter.

U.S. President Donald Trump revealed on his social media at the end of October that he had approved South Korea’s construction of nuclear submarines. He also indicated that these submarines, designed to carry conventional weapons rather than nuclear ones, are expected to be built at a shipyard in Philadelphia in the eastern part of the United States.

During the U.S.-South Korea summit that was held immediately before Trump revealed his decision, South Korean President Lee Jae Myung requested U.S. support for the development of nuclear submarines. Lee argued that South Korea’s existing diesel-powered submarines have low underwater navigation capabilities, restricting their ability to track North Korean and Chinese submarines.

Only six countries currently operate nuclear submarines: the nuclear powers of the United States, Britain, France, Russia, China and India. Compared to diesel-powered submarines, they can remain submerged for extended periods and have greater mobility.

China, in particular, possesses over a dozen nuclear submarines and routinely deploys them around Japan, in the South China Sea and elsewhere. North Korea aims to develop nuclear submarines capable of launching ballistic missiles.

Although past U.S. administrations have not allowed South Korea to possess nuclear submarines, Trump appears to have shifted U.S. policy in light of heightened military tension in the region.

The United States, Britain and Australia have already agreed that Washington and London will support Canberra’s deployment of nuclear submarines. This is also part of the effort to enhance deterrence against China.

Meanwhile, South Korea is seeking from the United States a supply of nuclear fuel, which is essential for the introduction of nuclear submarines. However, the current U.S.-South Korea nuclear agreement prohibits the use of U.S.-supplied nuclear fuel for military purposes, making it necessary to revise the agreement.

It is crucial for both the United States and South Korea to proceed with negotiations while ensuring transparency, so that the introduction of nuclear submarines does not invite concern or criticism about nuclear proliferation.

In Japan, an expert panel of the Defense Ministry proposed in September the introduction of submarines using “next-generation power,” with nuclear submarines in mind, as a measure to strengthen defense capabilities. Also, Defense Minister Shinjiro Koizumi said at a press conference that he would not rule out “any option” to enhance deterrence.

However, the Atomic Energy Basic Law limits the use of nuclear energy to “peaceful purposes,” and in general, it is said to be difficult for Japan to possess nuclear submarines under the current legal framework.

On the other hand, Japan is the only nonnuclear state that is granted the right to reprocess spent nuclear fuel and recover plutonium, and it publicly discloses their storage status. Japan should work to communicate well with the United States and South Korea, and it should aim to achieve both the maintenance of the nuclear nonproliferation structure and the strengthening of deterrence.

(From The Yomiuri Shimbun, Nov. 6, 2025)