The Republic of Korea (ROK), more commonly called South Korea, and the U.S. have been treaty allies since the end of the Korean War in 1953. We station troops and military assets there and conduct regular exercises with the South Korean military. Yet there is ambiguity about South Korea’s view of the U.S.‘s strong ties to and support for Taiwan.

Despite our close defensive partnership, South Korea openly acknowledges the One China concept — i.e. Beijing’s assertion that Taiwan is part of China. Taiwan takes strong exception to that notion.

If China attacks Taiwan, South Korea’s role in such a scenario is uncertain. That will be explored in more detail below.

ROK and Japanese relations were extremely strained in the past due to Japan’s colonization of the Korean peninsula from 1910 to 1945. Decades of Japanese abuse of Koreans were horrendous. However, in 2023, relations thawed with the signing of a three-party agreement between the U.S, Japan, and South Korea for expanded military cooperation and exercises, sharing of intelligence, monitoring information on threats from North Korea, and setting up a Secretariat for stronger diplomatic relations.

Its population of 52 million people ranks the ROK 28th in the world. It hits well above its weight, with a GDP that ranks 13th in the world. South Korea is one of the world’s largest producers of semiconductors and has one of the world’s largest shipbuilding industries, ranking either number one or two, depending on the year. It also builds many of the world’s best ships in large numbers. There are about two million Koreans in the U.S., of whom roughly one million are native-born.

The U.S. and ROK’s military ties are extremely close and long-lasting. We currently station 28,500 military personnel there, scattered among five bases. This is a very mature and long-standing commitment to defending South Korea against a potential attack from the north. The largest part of these military forces is from the Army, but all services are represented, including some special forces. In recent days, U.S. and South Korean forces began a major annual exercise, Freedom Shield, which will involve about 18,000 troops and test capabilities in information and cognitive warfare, a recent emphasis.

The Korean War military death toll was 137,000 South Koreans dead, 200,000-400,000 North Koreans dead, 200,000 Chinese dead, and 36,000 Americans dead. Even more civilians on both sides were also killed, the numbers in the millions.

Still today, the ROK worries foremost about its neighbor to the north, the Democratic People’s Republic of Korea (DPRK). During the Korean War, China was the primary patron and fighter on behalf of the North. And that malign patronage continues today. The People’s Republic of China functions as the protector and international supporter of the DPRK, and it harbors designs of conquest of the South. The DPRK would like nothing better than to take over South Korea and rule the Korean peninsula. However, the U.S. is pledged by a long-standing treaty to defend the ROK from the DPRK. The ROK is a nuclear power but does not have nuclear weapons. However, it is very advanced technologically and could develop nuclear weapons if it wanted to in short order. The nation uses nuclear power only for peaceful energy production.

According to a State Department report in January 2025, the U.S. has sold advanced weaponry to the ROK military including “MK 54 Lightweight Torpedoes, Precision Guided Munitions, the F-35 Joint Strike Fighter, P-8A Patrol Aircraft, Patriot Advanced Capability-3 missile systems, Global Hawk Unmanned Aerial Vehicle, KF-16 aircraft Upgrades, Aegis Combat Systems, Harpoon and Hellfire Missiles, and AH-64E Attack Helicopters.”

The Congressional Research Service says these contracts amount to over $30 billion and represent many of the U.S.’s most advanced military systems. The U.S. is a significant trading partner with South Korea, ranking second in its trade, while South Korea’s imports to the U.S. rank seventh.

The ROK’s shipbuilding capabilities are of particular interest to the U.S. at this stage. I have written extensively on the decline in the size of the U.S. Navy and the rise of China’s navy, the People’s Liberation Army Navy (PLAN), now by far the world’s largest and rapidly gaining in strength, advanced technology, and weapons. The PLAN has ~395 combat ships, plus a large and technologically advanced Chinese Coast Guard fleet of 1,275 ships of all types, including 225 large offshore vessels over 500 tons. In addition, the PLAN has at its disposal 240 active Maritime Militia vessels in the South China Sea under the control of the PLAN for all sorts of activities, including harassing ships of other nations.

Thus, it is of great interest to the U.S. that the ROK has a strong shipbuilding industry that could aid our Navy. The South Koreans have shown a strong desire to build and repair ships for the U.S. and have invested in U.S. shipyards that could be employed to build ships and perform vital maintenance and overhaul. These are promising trends for the long term.

For the first time, a Navy auxiliary, the USNS Amelia Earhart, is being repaired in a South Korean yard. In October 2025, Huntington-Ingalls and HD Hyundai Heavy Industries signed an agreement to jointly pursue contracts to build Navy auxiliaries. Hanwha recently bought a Philadelphia shipyard and is investing millions in upgrading it.

These are baby steps, and much more must be done in partnership with the ROK to increase our urgent need for both new construction and repair capacity.

What role might the ROK play in the defense of Taiwan if that becomes necessary? Historically, South Korea has been distant from anything related to Taiwan. That is slowly changing as the realization grows that anything that happens to Taiwan will inevitably affect it. Stability in the Taiwan Strait — or the lack of it — directly affects South Korea. So, the ROK has been quietly supporting statements about peace and stability in the region. Some analysts see a transition in the U.S.-ROK alliance from a peninsula-only focus to a broader regional perspective.

Another worrisome possibility is that China may foment action on two fronts to complicate the situation for the U.S. and our allies. For example, launching an action against Taiwan while simultaneously fomenting DPRK action of some sort against the South. This would pose a horrible dilemma for the leaders of the ROK. Defense analysts who assess such matters think the ROK would have a role in any U.S. defense posture it decides on regarding Taiwan. Most believe U.S. bases in Korea would be used for support in any conflict and that logistics, intel, and recon support would also be available. Preserving stability on the Korean peninsula would remain a number one priority.

We can be hopeful that the seeming success of Operation Epic Fury in Iran is giving China a lot to think about. Still, cultivating our strong defense relationship with the ROK and improving industrial partnerships to leverage its excellent shipbuilding capabilities and capacity are opportunities we must seize now to increase the size and readiness of our Navy.