The outbreak of World War II in 1939 found the United States, for the first time in its history, a neutral unconcerned with the defense of its rights at sea. It had, by drastic legislation enacted between 1935 and 1939, voluntarily withdrawn from the business of supplying the needs of the belligerents. It had also curtailed the travel of Americans on belligerent passenger vessels and had circumscribed trade with neutrals by keeping American ships out of certain areas, designated as combat zones, adjacent to neutral ports. It had, in short, surrendered its traditional insistence that the rights of neutrals be respected.
Before long, however, the country abandoned the role of passive and withdrawn neutral and became virtually a co-belligerent, supplying the Allied powers with the sinews of war. The restrictive legislation was repealed in November 1941 and a vast flow of American goods in American ships started moving across the Atlantic. Now the term "freedom of the seas" was once more on the lips of American statesmen as German submarines, operating in wolf packs, attacked the Anglo-American maritime lifeline. President Franklin D. Roosevelt said in May 1941:
All freedom—meaning freedom to live and not freedom to conquer and subjugate other peoples—depends on the freedom of the seas—for our own shipping, for the commerce of our sister Republics, for the right of all nations to use the highways of world trade, and for our own safety…. As President of a united, determined people, I say solemnly: we reassert the ancient American doctrine of the freedom of the seas.
He had already, in September 1940, labeled submarine warfare as defiance of the "historic American policy" for which, "generation after generation, America has battled … that no nation has the right to make the broad oceans of the world … unsafe for the commerce of others." And in August 1941, when Roosevelt and Prime Minister Winston Churchill drew up the Atlantic Charter, a blueprint for the postwar world, the seventh of eight principles was the hope that "such a peace should enable all men to traverse the high seas and oceans without hindrance." Thus, the two leaders reiterated the broad concept of the freedom of the seas first proposed by Woodrow Wilson.
Like the Treaty of Versailles, which ended World War I, the several treaties negotiated after World War II made no mention of the freedom of the seas; and as the Covenant of the League of Nations had ignored the principle, so did the Charter of the United Nations. Thus, the hope of Franklin Roosevelt suffered the same fate as did the dream of Woodrow Wilson. The unrestricted right of all people to enjoy the freedom of the seas is still not guaranteed by international agreement. Indeed, since the end of World War II the United States has on three occasions taken actions that tended to limit the use of the seas by other nations. The first time was in June 1950, at the outbreak of the Korean War. President Harry S. Truman ordered the Seventh Fleet to patrol the Formosa Strait to prevent the Chinese communists from attacking Formosa and to keep the forces of Chiang Kai-shek from mounting an assault on the mainland. The Soviet Union promptly labeled the action a blockade, which the United States as promptly denied. As evidence to support its contention, America pointed to the fact that commercial traffic in the strait was unimpeded and untouched. The interdiction applied only to naval forces.
The second occasion came in October 1962, when President John F. Kennedy, upon learning that the Soviet Union had built missile sites in Cuba and had supplied Cuban premier Fidel Castro with missiles, proclaimed his intention "to interdict … delivery of offensive weapons and associated material to Cuba." He called the policy a "strict quarantine," yet it had all the markings of a blockade. Vessels were to be stopped, visited, and searched within certain prescribed zones and along certain routes. The Soviets considered it a blockade and protested on the ground that a blockade could be instituted only in wartime. To escape that anomaly, American lawyers called it a "pacific blockade," which international law permits as a means for one nation to seek redress, short of war, from another. The legal difficulty surrounding the use of that term was that in a pacific blockade only the blockaded nation's ships could be stopped and seized—not those of a third party. In this instance Soviet ships were the object of search and seizure. Whatever the terminology, it was clear that the United States had used naval forces to interfere with shipping on the high seas, albeit for the lofty motive of self-defense.
The third example of postwar American practice centered on President Richard M. Nixon's mining of North Vietnamese ports in May 1972. Again there was confusion as to the legal status of the act. Nixon denied the Soviet allegation that it was a blockade. The New York Times called it a "semi-blockade." The difficulty was compounded by the fact that the action took place not on the high seas but within the "internal and claimed territorial waters of North Vietnam," to use the words of the Department of State's legal officer. And, indeed, there was no interference with freedom of navigation beyond North Vietnam's territorial waters. Judged by the classic nineteenth-century definition of blockade, the act could not be called a blockade. But by the mid-twentieth century, many of the traditional and historic concepts that made up the doctrine of the freedom of the seas were being altered to suit new conditions of international relations.
One major change concerned the extent of territorial waters. For centuries, the territorial waters of a state were calculated at three miles (a cannon's range). At a conference held in 1930 at The Hague for the codification of international law of the sea, the three-mile limit was adopted officially and the marginal sea was declared to belong to the state. At the same time, several nations, wishing to exploit, without competition from other nations, extensive fishing beds and mineral resources in the subsoil, made claims to a more extended area—up to two hundred miles. The United States made no such claims, but in 1945 President Truman announced the creation of "conservation zones in those areas of the high seas contiguous to the coasts of the United States" for the development of fishing. Similarly, the continental shelf in the same contiguous areas was to be exploited for its natural resources. No specific limits were put on the contiguous areas, but it was known that the government favored an extension of the territorial waters from three to twelve miles and the creation of an economic zone of two hundred miles.