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Maritime Security on the Korean Peninsula: The Story of the Northern Limit Line

On July 28, a North Korean fishing vessel crossed over the Northern Limit Line (NLL), a disputed maritime demarcation line, into South Korean waters under very mysterious circumstances. However, this was not the first North Korean vessel to cross the NLL in 2019 under auspicious circumstances. In mid-June, a small wooden vessel crossed over the maritime border and, three days later, docked in the South Korean port of Samcheok.

Bow section of a PKM 301 Chamsuri class patrol boat. Image courtesy of Mztourist. ©2011

These two vessels are emblematic of a larger trend; between May 31 and July 14, 380 North Korean vessels were expelled crossing the Northern Limit Line, according to the South Korean Joint Chiefs of Staff. With the Northern Limit Line still heavily contested, there is a fear that even the smallest incident may spark violence on the Korean Peninsula.

The Northern Limit Line, or NLL, was created shortly after the end of the Korean War in August 1953 to ensure South Korean fishing and naval vessels did not venture far enough north to spark clashes. Two decades after its inception, North Korea lodged its first complaint against the NLL at the Military Armistice Commission Meeting in December 1973. During the meeting, the North Korean representative argued that several islands rested in North Korean territorial waters, a claim rejected by the commission. Even after having its claim rejected, the NLL remained quiet for decades.

Violence first occurred across the NLL on June 15, 1999 when a North Korean vessel opened fire on a South Korean naval vessel. During the brief clash, 30 North Korean sailors were killed, four North Korean ships were damaged, and a North Korean torpedo vessel was sunk. South Korea suffered less casualties; 5 patrol ships were damaged, and 9 sailors wounded. A few months after the clash, North Korea proposed a new maritime border which provided South Korea some access to the islands. Despite Washington, Seoul, and Tokyo rejection of the proposal, North Korean ships violated the NLL on a less frequent basis following the initial clash.

In the new millennium, violence across the NLL has increased. In 2002, a 20-minute exchange of fire between South and North Korean navies resulted in the sinking of a South Korean vessel and the disabling of a North Korean ship, as well as wounding approximately 50 sailors. Again, in 2010, two major incidents resulted in the loss of life along the NLL. On March 26, a North Korean torpedo sunk the Cheonan, a South Korean naval ship, killing 46 sailors. In November, North Korea fired on the South Korean island of Yeonpyeong, wounding approximately 20 people.

With a rise in violent interactions across the NLL, a few important questions need to be answered. What exactly is at stake when it comes to the NLL? How do South Korea and North Korea defend their claims along the contested maritime border? And finally, is there a way the two Korea’s can work to maintain peace along the NLL?

When it comes to the NLL, four major issues feed the dispute. Economically, the NLL is ripe with valuable fishing resources and can provide an easy route for inter-Korean economic cooperation. Another key issue is state sovereignty. Currently, it is unclear if the NLL is acting as a military demarcation line to prevent conflict or if it is a territorial dispute between two sovereign states. Finally, the NLL presents a strong security challenge as both Koreas have expressed anxiety over the close proximity of the two navies and worked to grow their defense capabilities in the region.

Countering these challenges has been a strong feature in South Korea’s defense policy. In the 2018 Defense White Paper, South Korea said its military “maintains a full readiness posture to firmly defend the ROK’s entire territorial land, water, and airspace…including the five northwest islands,” which sit just below the NLL. In order to maintain its readiness, the South Korean Navy replaced its aging boats with state-of-the-art vessels to patrol the NLL and took serious action against those responsible for a security lapse earlier this year.

North Korea also maintains a strong military presence around the NLL. To enhance its posture along the NLL, the Korean People’s Army constructed facilities to house coastal artillery units on Gal-do Island, just 2.4 kilometers north of the NLL. This base increases North Korea’s military capabilities and presents a challenge to South Korea’s military as it increases the amount of monitoring required for effective defense of the NLL.

With the rise in tensions across the NLL over the past decade, there is little to indicate a possible path to solution. However, as the inter-Korean, as well as the United States-North Korean, relationship improves, it may be possible for a diplomatic solution to be presented. For example, Moon Jae-in could accede to some North Korean demands along the NLL in return for some steps toward denuclearization. Pursing this strategy provides the Moon administration a path to defusing tensions on a variety of fronts, while also gaining much needed steps toward an eventual North Korean denuclearization.


Benjamin Zimmer

Benjamin is a Master of International Affairs student at The Bush School of Government at Texas A&M University where he focuses on East Asia and intelligence. He is the creator of The Korea Page: News and Analysis from the Korean Peninsula. His research interests include North Korean politics, the North Korea-United States relationship, and nuclear proliferation. His writings have appeared in The Peninsula Report, Foreign Policy Press, and The Sphere. He can be found on twitter at @bzimmer8.

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