South Korea does not need nuclear subs

South Korea is again debating whether to develop and build a nuclear-powered submarine.

During a National Assembly confirmation hearing that took place last week, Admiral Kim Myung-Soo, the nominee for chairman of South Korea’s Joint Chiefs of Staff, responded positively to a question about the utility of nuclear-powered submarines, stating that “those capabilities are needed.” He noted, however, that the current U.S.-Korean nuclear agreement restricts the use of nuclear materials for military purposes.

Nevertheless, there appears to be a growing sentiment on the part of both of South Korea’s leading parties and the general public in favor of Seoul acquiring nuclear-powered boats. The government should resist the temptation to do so.

In theory, South Korea could avoid America’s restrictions by turning to France to help it develop or acquire a nuclear-powered submarine. France could help South Korea develop its own nuclear-powered sub, much as Paris has assisted Brazil with its own nuclear-powered submarine program.

However, there are many reasons why Seoul should not imitate the Brazilians and forge ahead with its own program. To begin with, it was only in April of this year that President Biden and South Korean president Yoon Suk Yeol reached an agreement that not only calls for greater consultation on nuclear matters between the two countries, in the form of a newly created nuclear consultative group, but also provides for an enhanced American nuclear presence around the peninsula to deter North Korean aggression.

In that regard, in mid-July a U.S Navy Ohio-class nuclear-powered ballistic missile submarine made a port visit to Busan, the first such visit in decades. Were South Korea to attempt to evade its long-standing commitment to Washington to concentrate all its nuclear-related efforts solely for civilian purposes, it would undermine the spirit of the Biden-Yoon agreement and create a serious split between the two countries — from which only the North Koreans would benefit.

In any event, it is not clear how Seoul could afford to undertake a nuclear-submarine program unless it were to dramatically increase its defense spending beyond current levels. Indeed, the South is pressing ahead with a new 50,000-ton aircraft carrier that is certain to cost billions more than its 30,000-ton carrier. Seoul has seriously underestimated the cost of the smaller carrier, which it set at approximately $2.1 billion; the larger carrier easily could cost more than $6 billon. Given the government’s commitment to the aircraft carrier, the costs it has already sunk into that program, plus other key elements of its defense budget, it’s hard to see how Seoul would find additional funds to produce a viable nuclear-powered submarine fleet.

If Seoul were to launch a submarine program, it would have to build at least three boats to ensure that one boat operates on station at all times. Three submarines are likely to cost more than $10 billion once logistics support, including special safety provisions for the handling of nuclear materials, is taken into account. Indeed, for South Korea to field a credible fleet it would have to ensure that two subs are always on station, meaning that both the total number of boats to be acquired, and their corresponding costs, would have to double.

It is not at all clear that the government can increase its already significant defense spending levels by additional tens of billions of dollars. Finally, as the extended AUKUS timeline for fielding Australian submarines clearly indicates, more than a decade would pass before a single South Korean nuclear submarine actually took to sea.

Lastly, there are good operational reasons why South Korea should continue to acquire conventionally powered submarines rather than nuclear powered boats. The waters around the Korean peninsula are relatively shallow, which favors the employment of quiet conventional subs. South Korea now operates seven Son-Won II–class diesel-electric submarines, powered by a hybrid diesel‐electric/fuel cell with air-independent propulsion technology. These subs are extremely quiet; they can travel up to 20 knots when submerged and remain under water for seven weeks. They are perfectly suited for operations around the Korean Peninsula.

The South is currently planning both to upgrade the Son-Won II for about $100 million per boat and is proceeding with a new Son-Won III class at about $900 million per submarine. In other words, the country could acquire three state-of-the-art conventional submarines for less than the cost of one nuclear-powered sub.

The costs, the technologies, and operational realities all weigh against South Korea acquiring nuclear-powered submarines. If that were not enough, America’s recent commitment to bolster the nuclear umbrella that it has long provided to South Korea and that is so critical to its deterrent should settle the argument once and for all.

Dov S. Zakheim is a senior adviser at the Center for Strategic and International Studies and vice chairman of the board for the Foreign Policy Research Institute. He was undersecretary of Defense (comptroller) and chief financial officer for the Department of Defense from 2001 to 2004 and a deputy undersecretary of Defense from 1985 to 1987.