Following North Korea's third nuclear test, national polls in South Korea have found more than 60% of those surveyed believe the South needs its own nuclear weapons.
As the North moves closer to fielding nuclear weapons, many in South Korea rightly view that the country's national security strategy of deterring the North by maintaining a smaller yet qualitatively superior conventional military force dependent upon support from the United States is no longer sufficient. The US extended deterrent was even referred to as "an umbrella with holes".
Doubts about the strength of South Korea's deterrent and the US commitment to fully carry out its alliance obligations should not be dismissed as unfounded fears triggered by North Korean provocations. Rather, steps to address the increasing gap in the strategic military balance between the two Koreas must be taken.
For South Korea, deterrence against even a non-nuclear North Korea is inadequate. Despite the alliance with the US, Pyongyang initiated numerous attacks throughout the 1990s and 2000s resulting in multiple South Korean warships sunk and civilian fatalities. With North Korea's quantitative military advantage and stockpiles of chemical and biological weapons, South Korea relies heavily upon extended deterrence provided by the US, including the nuclear umbrella. Pyongyang's fielding of nuclear weapons would deteriorate existing deterrence in terms of force strength.
North Korea's advancing nuclear programme challenges the credibility of the US commitment to South Korean security. There is no need to doubt the sincerity of statements by US leaders affirming a strong alliance and deterrence. However, in the past, even before the North Korean nuclear problem surfaced, changing circumstances, even on political grounds, have jeopardised the integrity of the alliance; this is best illustrated by the events of the 1970s. President Jimmy Carter aimed to withdraw all United States forces in Korea. Senator George McGovern also called for a complete withdrawal, labelling the alliance a potential liability that could "trip" Americans into "another war in the wrong place at the wrong time". Having served as the acting First Lady of South Korea during that time, President Park Geun-hye is well aware of those events.
The chance of history repeating itself is not negligible, especially against a nuclear-armed North Korea. For example, in the commonly speculated worst-case scenario in which North Korea invades Seoul and ceases all hostile actions before calling on the US to sign a peace agreement or risk a nuclear attack, no one can be certain if US leaders would have enough political capital to rally the US public and fight against the North.
South Korea must acquire new capabilities to field a strengthened deterrent against a nuclear North. The three most discussed proposals since the recent test are: 1) nuclear armament, 2) redeployment of US tactical nuclear weapons, and 3) deployment of submarine-launched cruise missiles.
Independent nuclear armament is difficult to achieve. One of many hurdles is South Korea's high degree of dependence on trade, which reached 113% of gross national income in the first quarter of 2012. Any trade sanctions imposed on the South due to nuclear weapon development will devastate the economy. Second, returning US tactical nuclear weapons to South Korea is also problematic as it would ultimately require Washington's approval for use. Finally, deployment of cruise missiles launched from submarines looks promising, although improvements are needed.
Exactly two days after the test, South Korea's Ministry of National Defence (MND) revealed deployment of the ship and submarine launched cruise missile Haesung-II. The MND did not release specifications of the missile, but expert estimations put the range at about 1,000km when armed with a 500kg conventional warhead. The MND spokesman stressed that Haesung-II can be fired underwater without detection and strike through windows of North Korea's military installations. For this option to be a significant deterrent measure, however, technical advancements and changes in the operational concept are required.
North Korea has strong sea mine laying capabilities that expose South Korean navy ships and submarines to the risks of immobilisation or damage. Also, North Korea's attack submarines pose problems for cruise missile-armed South Korean submarines to venture close to a target. Increasing the range beyond 1,500km will give South Korean submarines a buffer, enabling the firing of missiles well south of Jeju Island in international waters. In attacking North Korea's command and control centres or leadership bunkers, a conventional 500kg warhead would not be able to penetrate and destroy hardened or underground facilities. Therefore, South Korea should develop bunker-buster warheads, the feasibility of which was demonstrated by the US navy's Tomahawk cruise missiles.
Operationally, the navy needs to accelerate acquisition of KSS-III class submarines, which can carry more cruise missiles than the current Son Won-il class. Also, submarines designated for deterrence roles should be operated at all times, rather than only during crises. Enhancing survivability and lethality of Haesung-II armed submarines would give South Korea a conventional independent strike capability that would contribute to strengthened deterrence.
Deployment of long-range bunker-buster cruise missiles onboard submarines pose threats to the region. However, China possesses DH-10 cruise missiles and it has a secure second-strike nuclear capability. For Japan, the new threat could provide an additional reason to procure offensive weapons, possibly sparking a regional arms race. Nevertheless, given the prospect of its official enemy acquiring nuclear arms, worrying about instigating a regional arms race due to measures taken for self-defence cannot be a high priority for South Korea.
Proposing the acquisition of independent conventional military capabilities against the North in preparation for worst-case scenarios should not be construed as dismissing the importance of the alliance with the US. The alliance has been successful in deterring a full-scale war. Seoul's enhanced ability to strike Pyongyang would lessen the burden on Washington, contributing to a more flexible and durable alliance.
Richard Seok-ho Kang is a non-resident Kelly Fellow with the Pacific Forum CSIS and a former military intelligence officer for South Korea's Ministry of National Defence. This article originally appeared in the Pacific Forum CSIS Pacnet series.