The territorial sea is a marine space under the territorial sovereignty of the coastal State up to a limit not exceeding 12 nautical miles measured from baselines. The territorial sea comprises the seabed and its subsoil, the adjacent waters, and its airspace. The landward limit of the territorial sea is the baseline. In the case of archipelagic States, the inner limit of the territorial sea is the archipelagic baseline. The outer limit of the territorial sea is the line every point of which is at a distance from the nearest point of the baseline equal to the breadth of the territorial sea.
At present, some 137 States Parties to the LOSC have established a 12-nautical-mile territorial sea, and approximately ten States have claimed, wholly or partly, a territorial sea of less than 12 nautical miles. Some twenty-four States that formerly claimed a territorial sea more than 12 nautical miles in breadth have pulled back its breadth to 12 nautical miles. Only nine States, including four parties to the LOSC, claim a greater breadth than 12 nautical miles. Nonetheless, those claims have encountered protests from other States. Considering that the 200-nautical-mile EEZ is currently well established as customary law, it may be said that the 200-nautical-mile territorial sea is contrary to international law. Overall, it seems that the 12 nautical miles maximum breadth of the territorial sea is now established in customary international law. While the LOSC contains no rule relating to a minimum breadth of the territorial sea, no State has claimed a territorial sea of less than 3 nautical miles in practice.
In addition, roadsteads which are normally used for the loading, unloading and anchoring of ships, and which would otherwise be situated wholly or partly outside the outer limit of the territorial sea, are included in the territorial sea. In practice, there seem to be few areas more than 12 miles from the baseline that are suitable for the loading, unloading and anchoring of ships. Hence it appears that roadsteads have only a minor role in determining the spatial scope of the territorial sea.
Concerning the judicial character of the territorial sea, the Court of Arbitration, in the 1909 Grisbadara case between Norway and Sweden, stated that ‘the maritime territory is an essential appurtenance of land territory’ and ‘an inseparable appurtenance of this land territory’. According to Judge McNair, ‘the possession of this territory [territorial waters] is not optional, not dependent upon the will of the State, but compulsory’. There is no doubt that the territorial sea is under the territorial sovereignty of the coastal State. As explained earlier, territorial sovereignty in international law is characterised by completeness and exclusiveness. Accordingly, the coastal State can exercise complete legislative and enforcement jurisdiction over all matters and all people in an exclusive manner unless international law provides otherwise. At the same time, under Article 2(3) of the LOSC, sovereignty over the territorial sea is subject to the Convention and to other rules of international law. As will be seen next, coastal States’ sovereignty over the territorial sea is restricted by the right of innocent passage for foreign vessels.