Illustration by Elene Muradian.
The outbreak of war between Russia and Ukraine has once again shined a spotlight on the Montreux Convention, the 1936 treaty which regulates the transit of merchant and navy ships between the Black Sea and Mediterranean through the Bosphorus and Dardanelles straits. The convention guarantees unhindered access to merchant ships, but gives Turkey discretion on allowing the passage of warships during times of war. Turkey exercised this discretion during WWII, the 2008 Russo-Georgian War and during the current 2022 Russian Invasion of Ukraine.
The Montreux Convention was signed on July 20, 1936, between the states bordering the Black Sea—Bulgaria, Romania, the Soviet Union, and Turkey—as well as Britain, France, Greece, Japan, and Yugoslavia. After the dissolution of the Soviet Union, Ukraine and Georgia also became independent littoral states of the Black Sea. The Montreux Convention regulates the transit and navigation of ships between the Mediterranean and Black seas, at the same time safeguarding the security of Turkey and the other littoral states of the Black Sea.
There are separate regulations for merchant vessels and warships. Although Turkey can restrict the passage of warships during times of war or if it feels a threat to its own security, in time of peace it has to grant unrestricted passage to all ships, regardless of the flag they are bearing. There are, however, some restrictions regarding time spent in the Black Sea and the tonnage of ships; all ships passing through the straits must also undergo mandatory sanitary inspections. Warships crossing the straits have to notify Turkey in advance through diplomatic channels. Turkey is also allowed to impose a charge on ships passing with a non-stop over. Other than some general predetermined charges, the Montreux Convention specifies that Turkey cannot charge transit fees to merchant vessels, unlike other globally-significant waterways under one state’s control like the Suez and Panama canals.
From Sevres to Montreux
The Bosphorus and Dardanelles straits link the Black Sea to the Sea of Marmara and the Mediterranean; they also divide the European and Asian parts of Turkey. Thus the straits are considered to be Turkey’s internal waters; however, due to their international significance, Turkey has conceded to international cooperation to provide unhindered passage to ships through the straits, through the Montreux Convention.
The choke point of the straits has long been a matter of contention between Great Powers. The Ottoman Empire had controlled the waterway since its conquest of Constantinople (modern-day Istanbul) in 1453. They prohibited passage to foreign ships, as part of a general policy of restricting the trade between Europe and Asia. (Incidentally, this was the main trigger for Christopher Columbus to attempt to find an alternate route by sailing west.)
With its loss in the First World War, the Ottoman Empire was forced to concede its sovereignty over the straits. Both Greece and Russia coveted it, but Britain, as the pre-eminent naval power at the time, proposed an internationalized Zone of the Straits, which it would oversee similar to Gibraltar, Suez and Singapore. This arrangement was agreed to by the Ottoman Empire with the Treaty of Sevres in 1920.
However, Kemalist forces rejected the terms of the Treaty of Sevres and reconquered territory that the Ottomans had given up, including the Zone of the Straits, eventually declaring the Republic of Turkey in 1923 and signing their own peace agreement with the Allies in 1924, with the Treaty of Lausanne. While sovereignty of the territory was once again granted to Turkey, the Treaty of Lausanne included a “Convention Relating to the Regime of the Straits and Turkey”. It upheld international access through the straits and set up a commission responsible for their administration. The straits were also demilitarized such that Turkey was not allowed to deploy armed forces nearby, including the shores of the Sea of Marmara. Before the outbreak of the Second World War, Turkey requested a review of the clauses of the Treaty of Lausanne regarding the straits, which resulted in the adoption of the Montreux Convention in 1936. With this convention, which is still in force today, the demilitarized status of the straits was removed. Access to merchant ships would remain unhindered, while Turkey would be able to regulate the passage of warships during wartime.
Implementation of the Montreux Convention
The Montreux Convention and Turkey’s willingness to abide by its rules were tested just a few years after the convention was signed, with the outbreak of the Second World War. Although Turkish sources claim that Turkey tried to implement the convention to the best of its abilities during the war, the Allied forces complained several times that Turkey had provided passage to warships belonging to the Axis Powers, especially those sailing under the flag of Italy.
The Montreux Convention became an issue of discussion again during the 2008 Russo-Georgian War. During this conflict, the U.S. used its ships in the Black Sea to pass humanitarian aid to Georgia. But when the U.S. requested passage of two large hospital ships, Turkey denied the request. Turkish President Abdullah Gul told U.S. officials that allowing access to U.S. warships into the Black Sea would be too risky, as it would put the military vessels of two great powers into dangerous proximity.
The application of the convention became a topic of discussion again during Russia’s ongoing invasion of Ukraine. Following the Russian attack on February 24, 2022, Ukraine applied to Turkey to implement the respective articles of the Montreux Convention and block access to Russian ships attempting to enter the Black Sea, from which Russia was attacking Ukraine’s southern ports. After Turkey called Russia’s attack on Ukraine a “war” on February 27, Turkish Foreign Affairs Minister Mevlut Cavusoglu announced that Turkey would not grant passage to warships from either side of the conflict into the Black Sea. However, the ban has its limitations; if a warship of a littoral state of the Black Sea claims that it is returning to its port of origin, its passage cannot be impeded. Thus, some Russian warships were still able to transit through the straits as they claimed to be returning to their own ports.
Is the Montreux Convention Still Relevant?
The Bosphorus and Dardanelles straits are not only strategically important in times of war, they are also economically significant. About 3 percent of the global daily supply of oil, more than 3 million barrels, pass through the straits, mainly originating from Russia, Azerbaijan and Kazakhstan. Large quantities of iron, steel and agricultural products are also shipped from the Black Sea coast to Europe and the rest of the world through the straits. Given the significance of the straits for the global economy, Turkey has limited control over non-military vessels passing through the straits. In times of war, although it can ban the passage of warships, merchant ships can still pass through without restrictions.
Regardless of how much authority Turkey has over the straits, given the economic and strategic significance of the Bosphorus and Dardanelles, the power to implement the Montreux Convention emphasizes the strategic importance that Turkey retains due to its geography, and this notion plays a key role in shaping Turkish diplomacy.
Although the Montreux Convention was signed more than 80 years ago, when the world order and the geopolitical situation in the region were very different, there are concerns that scrapping it would take the situation back to the pre-WWI arrangement, when the Ottoman Empire had unrestricted control over them. The convention does give Turkey certain authority and enhances Turkey’s geopolitical role. However, its main impact is in actually mitigating Turkish discretion and facilitating international trade.
Currently, there are no substantial talks of amending or replacing the convention. However, in recent years, the Turkish side has become more vocal about the environmental impact of international shipping, given the rising number of vessels that pass through regularly. In parallel, in 2021, Turkey began constructing the Istanbul Canal, which would provide a bypass to the Bosphorus Strait. It could potentially argue that the Montreux Convention applies only to the Bosphorus Strait and not the Istanbul Canal, once construction of the $15 billion project is complete, thus imposing transit fees on large ships that take this alternate route. In the event of a blockage on the narrower Bosphorus (remember the 2021 Ever Given incident in the Suez Canal), the Istanbul Canal could alter the arrangement of the Montreux Convention and set the stage for new negotiations.
1- Seydi, Süleyman & Morewood, Steven: “Turkey’s Application of the Montreux Convention in the Second World War,” Middle Eastern Studies, 2005.
2- Oral, N., et al: “The 1936 Montreux Convention,” Center for Strategic and International Studies (CSIS), 2016.
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