From Gunboat Diplomacy to Sanctions

Throughout history, naval power has been one of the most effective tools not only for winning wars but also for achieving political results without fighting. From the age of sail to the steam age, and from dreadnoughts to aircraft carriers, great navies have been able to change the decisions of capitals without needing to use their firepower. The saying attributed to the English Republican Oliver Cromwell, "A warship is the best ambassador," expresses this understanding in a very simple way. This idea would reach its peak in the British naval tradition after Nelson, becoming one of the fundamental foreign policy tools of the 19th-century imperial system. In the 20th century, the US adopted the same method on a global scale. Gunboat diplomacy is the use of naval power as a tool of coercive diplomacy in a crisis environment. In gunboat diplomacy, the intention to use firepower is clear. Throughout history, gunboat diplomacy has been the most flexible foreign and security policy tool for states.

Navies are the most effective and flexible forces that can be used from the very beginning of a crisis, thanks to their inherent flexibility, long-term operational capability, sustainable firepower, self-sufficiency, mobility, freedom to use the high seas, and the fact that they are not subject to restrictions such as requiring transit permission from land and air countries to reach crisis areas.

There is no need to obtain permission for deployment and transit at sea. Passage through foreign territorial waters, straits, and canals can be made via innocent passage and transit passage. Naval elements can create a profound psychological impact on public opinion and governments by appearing from over the horizon and through their impressive appearance. After reaching their targets, they can suddenly withdraw behind the horizon line and disappear from the public eye. However, even their presence beyond the horizon can affect the psychology of the public and governments at any moment.

Gunboat diplomacy, created by the material and abstract presence of a warship, involves the limited use or threat of use of naval forces—excluding wartime use—for the purpose of resolving an international or domestic issue in favor of our own state, or delaying material or moral damages that may arise due to this issue.

The person who put forward the modern theory of this method was the British diplomat and naval strategist Sir James Cable. In his work titled Gunboat Diplomacy: Political Applications of Limited Naval Force, published in 1971, Cable defined gunboat diplomacy as gaining an advantage or preventing a loss in an international dispute through the use or threat of use of limited naval force without reaching the level of war. For Cable, the issue was not necessarily about opening fire. The real issue was the warship becoming a visible and mobile representative of political will.

According to Cable, naval power could be used to create a fait accompli or to eliminate an existing one; to force the other party to change its behavior or policy; to create options and thus gain time during an escalating crisis and to keep the force capable of intervening in developments ready in the region; and finally, to demonstrate political determination and intent through the presence of warships. The summary of all of this was to coerce without fighting.

Coercion from the Sea in the Age of Empires

The 19th century is full of classic examples of gunboat diplomacy. The 1850 Don Pacifico Affair began when Britain used its navy to blockade Piraeus after Greece failed to meet the compensation demand of Don Pacifico, a Jewish businessman and British subject whose house in Athens was looted by a fanatical Orthodox Greek mob. Prime Minister Lord Palmerston defended the "Civis Romanus sum" understanding, which held that a British citizen would be protected by British power anywhere in the world. Despite the objections of France and Russia, he forced Greece to back down. The crisis was a classic example of gunboat diplomacy, where British naval superiority was converted into economic pressure and diplomatic results without declaring war.

In 1853–1854, American Admiral Matthew Perry forcing isolationist Japan to open its doors to trade with the US with his "Black Ships" fleet is another example. In 1902, when Britain, Germany, and Italy initiated a naval blockade against Venezuela for failing to pay its foreign debts and seized its warships and closed its ports to ensure the payment of debts, it became one of the classic examples of "gunboat diplomacy" where naval power was used for debt collection and political pressure. The targeted state was essentially presented with the choice of accepting the political demand or risking the consequences that the superior naval power off its coasts could create.

The fundamental element that made this system work was the military asymmetry between the great power and the target state. Most coastal states did not have a navy to respond on the high seas, long-range coastal defense systems, precision-guided missiles, unmanned aerial vehicles, submarines, or advanced mine capabilities. Therefore, the warship was not just a military platform, but an armed and visible representative of political will.

The Cold War and Aircraft Carrier Diplomacy

After the Second World War, gunboat diplomacy changed form. While the emergence of nuclear weapons made direct war between great powers extremely dangerous, crises, proxy wars, and limited conflicts continued in peripheral regions. It was precisely in this environment that navies became extremely useful tools for political pressure and power projection through conventional firepower. Sending a Carrier Strike Group (CSG) to a crisis region, the approach of an amphibious fleet to the coast, or the deployment of nuclear submarines to the region carried a political message in itself.

The Taiwan Strait crises of the 1950s, the 1958 Lebanon crisis, the implementation of a naval quarantine during the 1962 Cuban Missile Crisis, the sending of the USS Enterprise task group to the Bay of Bengal during the 1971 Indo-Pakistani War, and the dispatch of two American aircraft carrier groups to the region during the 1995–1996 Taiwan Strait Crisis were different examples of this tradition. Even in the proxy wars of the Cold War, gunboat diplomacy continued to live on.

Turkey and the 1974 Cyprus Operation

Turkey's 1974 Cyprus Peace Operation is also one of the important examples of naval power producing political results. Here, it is necessary to draw the line correctly in Cable's definition. After the operation moved to the actual landing and combat phase, the event went beyond gunboat diplomacy in the classic sense and became a direct military operation. However, the naval deployment before the operation, the formation of the landing force, and the presence of the Turkish Navy around the Island largely overlap with the logic of using limited naval force as an indicator of political pressure and determination, as described by Cable. Indeed, when Cable later discussed the 1974 Cyprus intervention alongside the Falklands example, he debated the impact of limited naval force on political decision-making mechanisms. For Turkey, the fundamental truth revealed by the Cyprus example is that naval power can be used not only to fight at sea but also to change political outcomes on land.

The Unipolar Era and the Golden Autumn of Gunboat Diplomacy

The unipolar era that emerged with the dissolution of the Soviet Union opened a new and very powerful field for gunboat diplomacy. There was no longer a Soviet Navy of equivalent scale globally to stand against American aircraft carriers. From the Adriatic to the Persian Gulf, and from the Mediterranean to the Indian Ocean, American naval power had an extremely wide freedom of movement. The approach of a carrier strike group to the shores of a state was a political event in itself. Because the aircraft carrier carried not only warplanes but also American political will. However, this period did not last forever.

The Arming of Coasts and the End of the Era of Impunity

One of the most important military transformations of the twenty-first century is the arming of coasts rather than warships. Long-range anti-ship missiles, ballistic and cruise missiles, quiet diesel-electric submarines, sea mines, unmanned aerial vehicles, kamikaze drones, unmanned surface vehicles, satellite reconnaissance systems, and network-centric target detection, tracking, and illumination capabilities have given coastal states, which were previously extremely weak, the ability to threaten the expensive platforms of great powers.

Thus, the cost asymmetry of armed conflict and war began to reverse. A multi-billion-dollar warship could now be threatened by a missile or UCAV hundreds or even thousands of times cheaper than itself. As a result, the privilege of approaching with impunity, which formed the psychological foundation of gunboat diplomacy, began to erode.

The area denial and access restriction (AD/A2) capabilities implemented by Iran in the Persian Gulf and the Arabian Sea, and by the Houthis in the Red Sea, are striking examples of this today. In the geography of the Strait of Hormuz and its surroundings, the distributed force structure consisting of shore-based missiles, UCAVs, mines, and small fast-attack craft has restricted the freedom of movement of large surface platforms. The Russia-Ukraine war in the Black Sea has created similar results. Ukraine, which does not have a strong classic navy, has been able to significantly limit the freedom of movement of the Russian Black Sea Fleet with coastal missiles, unmanned surface vehicles, and long-range UCAV systems. Therefore, in the coastal battlefield of the 21st century, dominating the sea and approaching the coast without cost no longer mean the same thing.

Sanctions Have Joined the Gunboat

With the rise in the operational cost of coercion via gunboat diplomacy from the sea in the classic sense, another coercion mechanism has increasingly come to the fore. This system, which we can also call sanctions diplomacy, is very different from the other. While a warship used to be sent in front of the target state's port in the past, today, a tanker carrying the state's oil can be branded under the name of a 'shadow fleet' without UN authorization, left uninsured, excluded from the financial system, banned from entering ports, prevented from receiving services from classification societies, and its companies and ships can be placed on sanctions lists. Thus, some functions of a physical naval blockade are increasingly being carried out with financial and legal blockade tools.

The sanctions system created against Russia and Iran is the largest laboratory for this today. Hundreds of ships have been placed on the sanctions lists of Western states on the grounds that they carry Russian oil. In response, Russia and the actors trading with it have created a large maritime transport system under the name of a shadow fleet using alternative insurance, flags, companies, and payment mechanisms. Thus, the sanctions struggle, which was initially carried out in the financial and legal fields, has begun to be moved back to the physical maritime domain.

From Sanctions to Physical Intervention

The year 2026 constituted an important threshold in terms of unilateral economic sanctions increasingly turning into physical coercion at sea. During the Ukraine and Iran wars, merchant ships placed on the sanctions lists of the US, UK, and some European states did not only face port, insurance, and financial restrictions; stop, inspect, and boarding operations supported by warships and military helicopters also came to the agenda. Ships, especially those alleged to be connected to Russia and Iran and defined as a "shadow fleet" in Western literature, became the primary targets of these practices.

The fundamental legal problem here is that being placed on a sanctions list by the US, EU, or UK does not create the authority to intervene in a foreign-flagged merchant ship on the high seas. These are not universal sanctions adopted by the UN Security Council, but unilateral or regional measures stemming from the laws of the relevant states. Therefore, the presence of a ship on these lists does not automatically grant third states the authority to stop and board that ship on the high seas.

Article 110 of UNCLOS is important for this reason. The basic rule on the high seas is the exclusive jurisdiction of the flag state. The right of a foreign warship to visit a merchant ship is tied to limited situations such as piracy, slave trade, unauthorized broadcasting, statelessness, or false flagging. Being a "sanctioned ship" or a "shadow fleet" ship is not one of the reasons for the right of visit listed in UNCLOS 110. The fact that Western states, in their interventions, do not consider the sanctions decision alone sufficient and resort to justifications such as the statelessness of the ship or the invalidity of its flag is actually an admission of this legal reality. Therefore, intervening in a foreign merchant ship with a valid flag on the high seas solely on the grounds that it is on a US, EU, or UK sanctions list creates a serious international legal problem. An opposing approach would mean that unilateral sanctions decisions are effectively turned into global maritime policing authority. The military consequence of this development has also emerged. Russia has begun to escort some sanctioned merchant ships with warships, providing military protection at sea against the intervention attempts of Western states. Thus, the issue of economic sanctions is being moved directly into the field of military contact between states. When there is a warship wanting to enforce sanctions on one side and a warship of another state protecting the merchant ship on the other, an economic sanction can easily turn into a serious maritime crisis.

The transformation of unilateral sanctions, for which there is no UN Security Council resolution, into physical intervention on the high seas by expanding the limited exceptions of UNCLOS erodes the principles of the freedom of the high seas and the exclusive jurisdiction of the flag state. This method, used today against Russia or Iran, could be used tomorrow by other states for other reasons. One of the important struggles of the coming period will therefore take place not only between ships at sea, but also over which legal rules will govern the high seas.

Conclusion: The New 21st-Century Order of Coercion from the Sea

Considering the development of approximately two hundred years, it is seen that the tools of coercion from the sea have not disappeared; on the contrary, they have changed form and become more complex. In the 19th century, the appearance of a warship off the coast of a target state could be enough to influence political will. In the 20th century, aircraft carrier task groups took on the same function on a much larger scale. In the first quarter of the 21st century, naval power is transforming into a new coercion mechanism integrated with sanctions lists, the financial system, the insurance regime, port bans, satellite surveillance, and military force capable of physical intervention at sea when necessary.

Gunboat diplomacy has not disappeared either. China's large-scale exercises around Taiwan and the constant naval presence of the US and its allies in the Western Pacific, Eastern Mediterranean, and the Persian Gulf are current examples of this. However, gunboat diplomacy is no longer implemented solely by the appearance of a warship. The declaration of large exercise areas through NAVTEX and similar navigation/safety notices, the creation of dangerous areas, the creation of maritime areas that are temporarily to be avoided or whose access is effectively restricted, and the exertion of pressure on the commercial and military use of certain regions through intensive air-sea exercises have also become parts of the modern repertoire of coercion from the sea. Although these do not legally mean a blockade or a declaration of sovereignty, they can turn into tools for creating a fait accompli at sea and sending political messages to the extent of their duration, scope, and the way they are supported by military force.

On the other hand, the absolute superiority of the old model has been broken. Coasts are no longer as vulnerable as they were in the 19th and 20th centuries. Thanks to long-range anti-ship missiles, ballistic and hypersonic systems, submarines, unmanned systems, and shore-based sensor networks, while the approach of an aircraft carrier or a large warship to the coast continues to carry a strong political message, it also creates a growing operational and even strategic risk. For this reason, especially for Western naval powers, the center of gravity of coercion is shifting from sinking the ship to preventing the ship from trading, from destroying the port to eliminating the right of entry to the port, and from a classic naval blockade to a financial, legal, and technological blockade.

However, the boundary between economic and legal coercion and physical naval power is also becoming increasingly blurred. As seen in the Ukraine and Iran wars, the stopping or boarding of merchant ships on unilateral sanctions lists by warships and military helicopters is the most dangerous stage of this transformation. The transformation of sanctions without a UN Security Council resolution into physical intervention on the high seas directly concerns the principles of the freedom of the high seas and the exclusive jurisdiction of the flag state. The absence of an independent category of right of visit in the form of a "sanctioned ship" or "shadow fleet ship" under UNCLOS 110 is particularly important. Russia's beginning to escort some merchant ships with warships shows how much the distance between economic sanctions and military confrontation between states has shortened.

Today, the warship (gunboat) is still at sea, but it is no longer alone. Alongside it are banks, insurance companies, satellites, sanctions lists, port states, lawyers, and exercises and dangerous areas declared via NAVTEX. The gunboat diplomacy of the 19th century is thus transforming into a multi-layered order of coercion from the sea in the 21st century, where economic, legal, technological, and military tools are used together. Yesterday, the warship was the most effective gray-colored ambassador. Today, when a warship sets sail, economic and legal power also accompanies it.