Freedom of navigation (FON) is a principle of law of the sea that ships flying the flag of any sovereign state shall not suffer interference from other states, apart from the exceptions provided for in international law. In the realm of international law, it has been defined as “freedom of movement for vessels, freedom to enter ports and to make use of plant and docks, to load and unload goods and to transport goods and passengers". This right is now also codified as Article 87(1)a of the 1982 United Nations Convention on the Law of the Sea.
History
Development as a legal concept
Freedom of navigation as a legal and normative concept has developed only relatively recently. Until the early modern period, international maritime law was governed by customs that differed across countries’ legal systems and were only sometimes codified, as for example in the 14th-century Crown of Aragon Consulate of the Sea (; ; also known in English as the Customs of the Sea). These customs were developed and employed in local jurisprudence, often cases in prize courts regarding the capture of goods on the high seas by privateers. Under the Consolato customs (and other contemporary codes), "enemy goods can be captured on neutral ships and neutral goods are free on board enemy's ships." This established a framework under which neutral shipping was not inviolable in time of war, meaning navies were free to attack ships of any nation on the open seas, however the goods belonging to neutral countries on those ships, even if they were enemy ships, were not to be taken. This legal custom, which hereafter will be referred to as the consolato rule, was long observed by England (later Great Britain), France, and Spain, as major naval powers.
New theories about how to run the maritime world, however, started to emerge as time went on and maritime trade, travel, and conquest by the great European naval forces began to stretch beyond of European waterways.Two main schools of thought emerged in the 17th century. The first, championed most famously by John Selden, promoted the concept of mare clausum, which held that states could limit or even close off seas or maritime areas to access by any or all foreign ships, just as areas of land could be owned by a state, limiting foreign activity there. Other notable supporters of this idea included John Burroughs and William Welwod. In the larger geopolitical context, mare clausum was backed by the major naval and colonial powers of the day, including Spain and Portugal. As these powers extended their reach to the New World and across Africa and Asia, they wished to consolidate control over their new empires and access to trade and resources there by denying other countries access to the sea routes leading to these areas. By quite literally closing off access to the seas using their naval muscle, these states would profit handsomely from the growing maritime trade routes and foreign colonies.
Meanwhile, the Dutch Republic, the dominant European trade carrier, championed a different rule, known as mare liberum (free seas), summarized as "a free ship [makes] free goods." This meant that even enemy goods, always excepting contraband, were inviolate in neutral bottoms (i.e. hulls), making neutral ships off-limits for attack on the high seas. For the Dutch Republic, this was essential in order to secure the safety and viability of their extensive trade network. This concept was coined by Hugo Grotius, a Dutch jurist and a founding father of international law. Grotius advocated for a shift in maritime norms that would make the high seas free for transport and shipping, regardless of the country of origin of the ship. This would represent not only a change in law, but also a fundamental shift in the perception of the maritime realm as something not to be owned, as land is, but rather as a shared resource. Behind this concept is a liberal view of sovereign equality, in which all states have equal access to the high seas, and a view of an interdependent world connected by the sea.
As the dominant naval powers of Spain and Portugal weakened, and international trade increased, Grotius’ mare liberum concept would come to be the accepted custom governing sovereignty at sea.