HISTORY OF THE MARITIME ZONES UNDER INTERNATIONAL LAW
FROM THE CANNON SHOT RULE TO UNCLOS
For hundreds of years, the marine environment was free from regulation of fishing, shipping, and
resource exploitation. Over time, coastal States (countries) had an increased interest in national
security and the enforcement of laws to protect its commerce and marine resources. As a result, a
balance was needed to maintain the freedom of navigation that many foreign maritime interests had
relied upon. This need for balance is captured in the history of the law of the sea.
The birth of a nation’s authority to control its coastal waters has been traced back to the sixteenth
century. In the seventeenth century, the father of international law and doctrine on the freedom of
the seas, Grotius, recognized the existence of a nation’s jurisdiction over the coastal waters that
could be effectively controlled from the land. The extent to which a nation could control its
coastal waters was largely based on the reach of its cannons on the shore. Thus, the 3 nautical mile
(nm) limit of the territorial sea resulted from what is often referred to as the “cannon shot” rule.
In the U.S., the creation of a territorial sea and contiguous zone date back to as early as the late
1700s in response to issues of national security and law enforcement at coastal areas, including a
1793 diplomatic note sent from Thomas Jefferson and legislation passed by Congress in 1799 to allow
the boarding of foreign flag vessels within 12 nm from the coast. This zone was known as “customs
waters” and was later called the “Contiguous Zone.” By 1930 the proprietary rights of the coastal
state over the resources of the territorial sea was well established, provided it did not interfere
with a vessel’s right of innocent passage. In 1945, President Truman issued a proclamation asserting
rights to explore and exploit the oil and gas resources of the continental shelf outside of the 3 nm
territorial sea. In 1953, the U.S. Congress enacted legislation over the federal and state control
of the continental shelf. In 1958, international conventions were concluded in Geneva on the
territorial sea, contiguous zone and continental shelf. The concept of a fishery conservation zone
was born in another Truman Proclamation but Congress did not enact laws regarding a 200 nm fishery
conservation zone until 1976. This evolved into a zone whereby a coastal nation had exclusive
control over all economic exploration and exploitation of the natural resources off its coast. By
1982, the custom of asserting a 12 nm territorial sea, 24 nm contiguous zone, and 200 nm EEZ was
codified in the United Nations Convention on the Law of the Sea (UNCLOS).
U.S. CONTROL IN MARITIME ZONES VS RIGHTS OF FOREIGN STATES
The U.S. proclaimed a 12 nm territorial sea in 1988, a 24 nm contiguous zone in 1999, and a 200 nm
EEZ in 1983, consistent with customary international law as codified in UNCLOS. This customary law
is a balanced compromise between a flag State’s interest in maritime shipping and a coastal State’s
interest in protecting and managing its coastal waters. The U.S. sovereignty over its terrestrial
lands extends to its internal waters and territorial sea, including the airspace above and the
seabed below. Subject to ancient customs where nations should provide safe harbor to ships in danger
or distress (force majure), the U.S. may restrict entry or travel through its internal waters. The
U.S. may also prohibit the entry into portions of the territorial sea, provided there is still an
area that allows for vessels to exercise their right of innocent passage through the territorial
sea. “Passage” through the territorial sea must be continuous and expeditious, although that may
include stopping and anchoring under certain circumstances. While warships are generally immune from
laws and regulations, the U.S. has the right to require foreign warships comply with U.S. laws. If
they don’t, the U.S. may order the foreign warship to leave its territorial sea.
The contiguous zone is a buffer to the territorial sea, and within it, the U.S. may exercise the
control necessary to prevent infringement of its customs, fiscal, immigration or sanitary laws and
regulation of territorial sea. In addition, the U.S. may regulate the removal of cultural heritage,
including foreign flagged vessels and nationals in its contiguous zone. It overlaps the EEZ which
extends from the territorial sea out to 200 nm. The U.S. does not exercise sovereignty in the
contiguous zone or the EEZ. It does have exclusive sovereign rights and jurisdicton for exploration
and exploitation of natural resources of the seabed, subsoil, water column, and air space in the
EEZ.
All of these zones have a common point of reference from which they are measured: the baseline. The
rules for determining the baseline under UNCLOS are substantively the same as those under the 1958
Convention, which the U.S. ratified in 1961. As a line that marks the inner limit of the territorial
sea and the outer limit of internal waters, the baseline is comprised of the low water line on NOAA
charts plus closing lines across legally-defined bays and rivers. The U.S. uses a normal baseline,
as opposed to a straight baseline because of its interests in preserving the freedom of navigation.
One of the most important facts for those relying on NOAA’s charts for the limits of these zones is
that the baseline and all of the zones are ambulatory. They are subject to change due to accretion
and erosion of the shore.