TERRITORIAL SEA is a belt of coastal waters subject to the territorial jurisdiction of a coastal state. The territorial jurisdiction of the coastal state extends to the territorial sea, subject to certain obligations deriving from international law; the most significant of which is the right of innocent passage by foreign ships. The distinction between the territorial sea, in effect an extension of exclusive coastal state sovereignty over its land mass and the high seas, a global commons beyond the reach of any state's jurisdiction, dates at least to the early eighteenth century in Europe.
A limit to the territorial sea of three nautical miles from the coast was accepted by many countries until the latter part of the twentieth century, including by the United States, which claimed a three-mile territorial sea dating from the beginning of the republic. A United Nations–sponsored conference in 1958 adopted four major multilateral agreements on the law of the sea, but failed to secure an international agreement on a compromise limit to the territorial sea. The United States, along with other maritime powers such as the United Kingdom, Japan, and the Netherlands, argued for the traditional three-mile limit so as to preclude coastal-state encroachments into the navigational freedoms of the high seas. A second UN conference convened in 1960 was similarly unsuccessful. The Third United Conference on the Law of the Sea, initiated in 1973, adopted a major new multilateral convention in Montego Bay, Jamaica, in 1982. That agreement confirmed the emerging trend toward a twelve-mile limit. Although the United States is not a party to the 1982 convention, President Reagan in December 1988 claimed a twelve-mile territorial sea on behalf of the United States.
According to the Montego Bay convention, which has emerged as the international standard even for those states not party to it, measurement of the territorial sea from convoluted shorelines may be made from baselines connecting headlands. Baselines are also used for bays and estuaries with headlands not over twenty-four miles apart, between outer points of coastal inland chains that enclose internal waters, and for historic bays to which territorial claims have been established by long and uncontested use.
The territorial sea is now but one component of a larger international legal regime governing the interests of coastal states in their adjacent waters. The United States, like many states, claims limited jurisdiction in a "contiguous zone" of twelve additional miles beyond the territorial sea to enforce customs, fiscal, immigration, and sanitary laws, and to punish violations of its laws committed in its territory or territorial sea. U.S. courts have supported the arrest of smugglers hovering beyond territorial waters with the intent to violate customs laws. Legislation authorizing a four-league customs-enforcement zone was protested by other countries, but during Prohibition several countries agreed by treaty to arrests within a one-hour sailing distance from shore.
Many countries, following President Harry S. Truman's proclamation in 1945, have claimed jurisdiction over continental shelves extending off their coasts. This form of jurisdiction extends to the seabed and not the water column above it, primarily for the purpose of exploiting resources such as oil and gas. The extent of the continental shelf may vary, depending on the shape of the sea floor. "Exclusive economic zones," which govern the use of the water column primarily for the purposes of fishing, may extend up to 200 nautical miles from a coastal state's baseline. In 1983 President Reagan claimed an exclusive economic zone of 200 nautical miles on behalf of the United States.
Jessup, Philip C. The Law of Territorial Waters and Maritime Jurisdiction. New York: Jennings, 1927.
See alsoInternational Law .