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January 1974

The West Coast Korean Islands

This document was made possible with support from Leon Levy Foundation



Central Intelligence Agency


Directorate of Intelligence

January 1974






  1. In recent months North Korea has begun what appears to be a deliberate series of provocations against South Korea in the offshore waters northwest of the port of Inch’on. Since late October 1973, North Korean naval craft have established a patrol pattern that threatens access to five island groups claimed by South Korea and occupied by South Korean civilian and military personnel.* The provocations have thus far been minor in nature – high speed approaches by North Korean patrol boats toward South Korean vessels and intrusions within the 3-mile-limit of South Korean islands. Neither side has yet fired on the other.
  2. The purpose of these North Korean actions surfaced at the 1 December 1973 meeting of the Military Armistice Commission when North Korea claimed the waters surrounding each of the five island groups -- Paengnyong Do, Taech’ong Do, Soch’ong Do, Yonp’yong Do, and U Do -- as part of its territorial seas (Map 1). P’yongyang demanded that prior permission be obtained for even civilian vessels to transit these waters and land at the islands. Although the United Nations Command (UNC) has not taken a position on the relative merits of the territorial waters claims, it has specifically upheld the right of free access to these islands.




* The island groups lie only 2 to 13 miles from the North Korean mainland, and one of the islands is within 1.3 miles of a North Korean island (Map 1). (All distances are stated in nautical miles.) Further information concerning these island groups is contained in the Appendix.


Comments and questions may be directed toXXXXXXX of the Office of Basic and Geographic Intelligence, Code 143, Extension 3057.

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  1. When the Korean Armistice was signed in 1953, the five island groups were occupied by United Nations forces. Although much closer to North Korean territory than to South Korea, they were specifically retained under UN military control by the provisions of the Armistice. South Korean military forces still are maintained on all island groups and civilians live on four of them; all island groups and civilians live on four of themgroups and civilians The Armistice Agreement also states that forces of both sides are to “respect the waters contiguous to the demilitarized zone and to the land area of Korea under the military control of the other side.” Contiguous waters, however, are not defined.


The Northern Limit Line and Hypothetical Maritime Jurisdiction (Map 1)


  1. A major complication in the dispute is the Northern Limit Line (NLL), established in a 14 January 1965 order of the Commander Naval Forces, Korea (COMNAVFORKOREA), and drawn between the five island groups and “hostile waters” considered to be under North Korean control.* A clear antecedent of this line, although not under the same name, was established in 1961 by the same commander. The sole purpose of the NLL was to avoid incidents by forbidding UNC naval units to sail north of it without special permission; in at least two places, however, it crosses waters presumed to be under uncontested North Korean sovereignty.
  2. The South Koreans have regarded the NLL as a seaward extension of the Demilitarized Zone (DMZ) and a de facto boundary between South and North Korea. The NLL, however, has no legal basis in international law, nor does it conform along some of its length to even minimal provisions regarding the division of territorial waters. It is binding only on those military forces under the command or operational control of COMNAVFORKOREA.




*COMNAVFORKOREA, a US Flag Officer, is Navy Component Commander of the UNC and has operation control over the Republic of Korea (ROK) Fleet. Seizures of South Korean fishing vessels off the east coast of Korea in the late 1950’s probably prompted the COMNAVFORKOREA to institute the NLL.


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No evidence exists that the North Koreans have ever formally recognized the NLL. South Korea maintains that the North has respected the NLL since the Armistice in 1953, although no documentation can be found to indicate that the NLL was established prior to 1960.

  1. The Armistice makes no provision for the delimitation of territorial seas, but Line A-B, drawn in and seaward from the Han Estuary, was used to indicate respective military control of the coastal islands (Map 1). With the exception of the aforementioned five island groups, all islands lying north and west of Line A-B were placed under the “military control of the Supreme Commander of the Korean People's Army and the Commander of the Chinese People's Volunteers.” All islands lying south of this line were retained under the military control of the CINCUNC.
  2. Although the NLL and Line A-B have some immediate importance, the major problems are posed by the territorial waters claims of each nation. The situation is complicated by the vagueness of North and South Korean methods of delimiting their respective territorial seas. Map 1 shows North Korea’s 12-mile territorial sea based on a straight baseline constructed along the coast and off-lying North Korean-controlled islands. South Korea’s 3-mile territorial sea is similarly depicted.*


*All baselines and territorial seas limits shown on the maps are hypothetical. They have been constructed, using accepted techniques of international law, in such a way as to maximize the probable claims of both nations.


Inland waters, landward from the baseline, are those over which a nation exercises the complete sovereignty it exercises over its land territory. Territorial waters or seas -- regardless of whether they are measured 3 miles, 12 miles, or some other distance seaward from a baseline -- form territory over which a nation has exclusive sovereignty conditioned only by innocent passage, the right of foreign vessels -- merchantmen and possibly warships in times of peace -- to pass through a nation’s territorial seas. The enjoyment of this right may depend on the observance of special navigation, customs, quarantine, and other regulations promulgated by the coastal nation.


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  1. The areas of potentially conflicting claims are obvious latent zones of conflict. All five island groups lie within North Korea's claimed territorial sea. In the absence of any bilateral agreement, legal as well as de facto rights of access to the islands remain unsettled. South Korea’s assumed 3-mile limit poses somewhat different potentials for overlapping claims. As depicted on the map, it lies within probable North Korean inland waters (where P’yongyang’s sovereignty is complete) in two places -- to the northeast of the western island groups and to the north of the eastern island groups. Although the overlap is small northeast of Paengngyong Do, the South Korean position is to enforce its rights up to the 3-mile limit. North of Yonp-yong Do there is a greater overlap. This is a particularly sensitive area because of North Korea’s desire for unimpeded access to its expanding port of Haeju.


Hypothetical Median Line (Map 2)


  1. A possible method of delimiting disputed Korean west coast territorial seas is the construction of a median line. Map 2 shows a median line based on de facto sovereignty and drawn in general conformity with prevailing international law and practice, equidistant between the North Korean coast (including islands) and the island groups under UN military control. The southward extension of this median line into the high seas would normally be used only to allocate areas on the continental shelf for resource exploitation. Solution of the territorial waters dispute by use of a median line would both assure preservation of South Korean access to the five island groups and enhance access from the high seas to the North Korean port of Haeju.


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Island Group

Number of Islands
and Islets


Economic Activities

Paengnyong Do



Agriculture, fishing, and salt extraction

Taech’ong Do



Agriculture and fishing

Soch’ong Do



Agriculture and fishing

Yonp’yong Do



Agriculture and fishing

U Do



Entirely military

















*Regular military forces are located on all island groups except Taech’ong Do and Soch’ong Do. The Homeland Defense Force, the closest South Korean equivalent to the National Guard, is stationed on all island groups except U Do. About 2,000 military personnel, including Homeland Defense Forces, are stationed on the five island groups.

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A Central Intelligence Agency assessment of the origins of the Northern Limit Line.

Document Information


CIA Records Research Tool (CREST), Document No. CIA-RDP84-00825R000300120001-7, National Archives and Records Administration, College Park, Maryland. Obtained for NKIDP by Jae-Jung Suh.


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