Russia increasingly is flexing its military muscle in the Black Sea. Last year, it shut off access for foreign ships to the Sea of Azov, connected to the larger Black Sea by the Kerch Strait. In March and April this year, Russian President Vladimir Putin sought to display his military’s might by massing 120,000 troops on the Ukrainian border, before backing off to a limited degree.

Moves such as this and others reportedly triggered an initial U.S. decision in April to send two warships into the Black Sea from the Mediterranean, via the Aegean and Turkish straits managed by Turkey under the 1936 Montreux Convention. The reported plans led to fears that growing tensions between NATO and Russia could turn into a military confrontation. Fortunately, the friction subsided when the United States changed plans and opted to keep its ships in the Mediterranean instead. But tensions rose again last month, when Russian vessels and aircraft harassed the U.K.’s HMS Defender, days before the United States and Ukraine hosted the 32-nation Sea Breeze 2021 naval exercise in the Black Sea as a demonstration of their determination to maintain the area  open to international maritime traffic. This year’s Sea Breeze was the largest yet in terms of participating nations.

These tensions coincide with the 85th anniversary of the Montreux Convention that has regulated merchant and military maritime traffic into and out of the Black Sea since 1936. Negotiated and signed by littoral states of the Black Sea (Bulgaria, Romania, the Soviet Union, and Turkey) as well as Britain, France, Greece, Japan, and Yugoslavia, at a time when Europe was drifting towards World War II, the convention today remains a solid example of a rules-based international order. Its implementation has been far from perfect, but the very fact that, for 85 years, there has been no attempt to revise it and that the international community continues to abide by its terms speaks volumes. As the trans-Atlantic alliance confronts the mounting Russian challenges to security and stability in the Black Sea, it should avoid steps and policies that risk undermining the Montreux Convention.

Protecting Merchant Shipping and Regulating Warships

The Montreux Convention was adopted on July 20, 1936. It reinstated Turkey’s territorial sovereignty and ended the demilitarized status of the Turkish straits (the Dardanelles and the Bosphorus and, for the purposes of the convention, the Sea of Marmara between them), all connecting the Aegean (and, by extension, the Mediterranean) to the Black Sea. The convention ensures free passage for merchant shipping during peace time. Unlike, for example, the Suez and Panama canals, Turkey cannot charge fees for transit, other than pre-determined “taxes or charges” outlined in an annex to the convention, though every ship must submit to sanitary controls.

In the case of warships, the convention lays down a set of provisions to regulate their passage through the straits. These provisions govern the mode of entry, duration of stay, and tonnage, as well as the nature of weapons (main gun calibers, to be precise) they can carry on board. These provisions apply differently depending on whether a passage occurs in peace or war time or when there is a threat of war. For each warship, advanced notification must be given to Turkish authorities, which in turn must inform representatives of the parties to the convention in Turkey about the pending passages. The stay of warships of non-Black Sea states is restricted to a maximum of 21 days, and the overall tonnage of all foreign warships transiting through the Straits cannot exceed 15.000 tons. Similarly, the total tonnage of non-littorals’ warships in the Black Sea cannot go over 45.000 tons at any time.

Such limits arguably are the crux of the convention, which aims to avoid great-power competition and wars reminiscent of the late 19th and early 20th centuries by limiting the presence of warships of rival naval powers in a relatively small maritime area.  In practice, they have negated the risk of escalation by restraining major powers’ ability to quickly shift naval forces to and from the Black Sea during international crises (more on that below).  Lightly armed auxiliary ships are exempted from some of the restrictions. Although the agreement generally favors littorals over non-littorals in terms of transit of warships through the straits, certain restrictions apply universally without regard to a littoral-non-littoral distinction. For instance, aircraft carriers or submarines (with few exceptions) are not allowed to enter the straits, regardless of their flag.

The convention was adopted initially for 20 years, with automatic renewal for five years at a time if no party calls for its revision (France is the depositary for this convention). The agreement also lays down the procedures to be followed for amending its terms. However, so far, no party has initiated this procedure. This can be considered a recognition that the convention has successfully tamed the destructive great-power rivalries of the past in the region and has acquired the status of an international customary regime. This is acknowledged in the United Nations Convention on the Law of the Sea (UNCLOS, Article 35.c), which implicitly recognizes the place of the Montreux Convention as part of codified law governing seas.

The Record on Implementation

Implementation of the Montreux Convention can be viewed in three distinct periods since the end of WWII. The first one marked by the Cold War and Soviet naval supremacy that led to the Black Sea being occasionally referred to as a “Soviet Lake.”  It was a period that started with Joseph Stalin’s demands on Turkey, in the closing days of WWII, to establish Soviet military bases along the Turkish straits. This demand was a major factor in propelling Turkey to eventually join NATO, though during this period, the country developed a practice of scrupulously implementing the Montreux Convention to avoid any bilateral conflicts with the Soviet Union.

Especially in times of tension, however, Ankara also diligently enforced the legal restrictions under the Montreux Convention in the other direction, too, by making sure that Soviet naval deployments to hot spots in the Mediterranean did not radically upset the overall balance of forces in that theater. A case in point was the Arab-Israeli War in 1973. The Soviets could increase their naval presence in the region only in increments due to the Montreux Convention restrictions. Such phasing of the Soviet deployments during this war helped prevent the escalation of tension between the U.S. Sixth Fleet and the Soviet Fifth Eskadra.

The collapse of the communist regimes in Bulgaria and Romania in 1989, followed by the dissolution of the Soviet Union in 1991, dramatically altered the geopolitical picture of the Black Sea. Bulgaria and Romania democratized and eventually became members of both NATO and the European Union. Ukraine and Georgia emerged as independent littoral countries, while for Russia, not only did its maritime jurisdiction zones shrink significantly, its naval prowess diminished. Its access to the large naval base in Sevastopol depended on the consent of Ukraine, with which Russia had to split the once mighty Soviet naval assets. The 1990s and early 2000s also coincided with Turkey embarking on a path of economic and political reforms that expanded its regional influence just as Russia entered a major period of decline. Turkey led efforts in the region to build a regional security architecture based on economic and functional integration projects accompanied with modernized naval capabilities.

Still, Turkey maintained its policy of neutrality in carrying out the Montreux Convention, and also resisted pressure from the United States and NATO to relax some of the limits of Montreux in a manner that would have allowed them a greater naval presence in the Black Sea. Instead, Turkey pursued a policy of balancing its membership in NATO with its interest in ensuring cordial and cooperative relations with Russia.

The geopolitical landscape shifted again during the third period of Montreux’s implementation, with Russia’s invasion of Georgia in 2008 on the eastern shore of the Black Sea and its 2014 annexation of Crimea and military support for separatists in Ukraine’s Donbas region. These attacks significantly enlarged Russia’s territorial access to the Black Sea, allowed it to reacquire the Sevastopol naval base, significantly modernized its naval capabilities, and boosted its missile force on the Crimean Peninsula.

The stunning developments led to growing calls for expanding NATO’s presence in the Black Sea, including one from the Turkish president, considered a major shift from established Turkish policy. The United States began pressing Turkey — as chronicled by retired academics, diplomats and naval officers — to adopt a more liberal interpretation of the Montreux Convention, especially during the crisis over Georgia. In a 2019 interview, former Turkish President Abdullah Gül recollected how the United States at the time had appealed for clearance to allow large U.S. warships to sail into the Black Sea, ostensibly to bring humanitarian assistance. Gül said he advised U.S. officials that allowing such access would be too risky, bringing heavy warships from two great powers into dangerous proximity. Again, Turkey persisted with its established policy of jealously guarding the convention from any breaches.

However, this practice today is once more under pressure.

Reinforced Threat Perceptions

Renewed Russian assertiveness in the Black Sea region and the growing Russian military presence in the Eastern Mediterranean (especially most recently via Syria) have reinforced threat perceptions within NATO. Those perceived escalating risks coincide with U.S. President Joe Biden’s “American is back” policy, marked by his determination to revamp the transatlantic alliance and push back on Russia more forcefully. This has already translated itself into the adoption of policy measures, at the NATO summit in June, to counter Russia in the Black Sea region.

Furthermore, in the context of the ongoing process of developing NATO’s 2030 strategic concept, the need to address Black Sea security and stability is attracting growing policy attention. Though so far there have been no indications of an official NATO attempt suggesting circumventing the terms of the convention, in the broader discussion of how to deter growing Russian assertiveness in the Black Sea, there have been calls for a marked increase in the U.S. naval presence in the Black Sea that could only be achieved if the convention is breached or its provisions are stretched to the limit, such as reflagging naval assets of other NATO members under the three Black Sea members’ flags. There have also been suggestions for the revision of the convention in a manner that would transform the status of the Black Sea to a regular open sea, permitting free access to it by warships too. These are developments that risk aggravating the already difficult security situation in the region.

An additional challenge comes from the Turkish President Recep Tayyip Erdoğan’s highly controversial “Canal Istanbul” project. That undertaking is intended to divert traffic from the congested Bosphorus Strait to an artificial waterway to be constructed west of Istanbul, connecting the Black Sea to the Marmara Sea. He spurred consternation in April with his claim that the canal has nothing to do with the Montreux Convention and that, thanks to the project, “Turkey will gain an alternative that is fully under its sovereignty and beyond Montreux’s limitations.” His questioning of the applicability of the convention to shipping through the canal can be taken as a manifestation of his general lack of appreciation and enthusiasm for a rules-based international order.

Domestically, a large group of former Turkish ambassadors and admirals objected to the canal project and to the president’s remarks. They apparently fear his remarks could suggest unrestricted passage via the canal for warships and that this would amount to breaching the convention, which in turn would undermine Turkish national security. There were also questions raised whether it would be possible to compel merchant shipping to use a fee-based canal instead of free passage through the Bosphorus. Internationally, Russian President Vladimir Putin’s reaction was swift and categorical: he told Erdoğan on a personal call that Montreux had to be preserved. Finally, when seen from the perspective of a Turkish foreign policy that in recent years has been criticized for having become increasingly erratic and unpredictable, Erdoğan’s remarks further undermine the trust of Turkey’s transatlantic allies with respect to managing an increasingly volatile security landscape in the Black Sea region.


Russia is indeed posing a major challenge in terms of the security and stability of Europe in general and the Black Sea region specifically. Considering the Russian invasions of Georgia and Ukraine, the Montreux Convention may not appear to them as having served their territorial security interests and needs. Yet, unregulated access to the Black Sea – as would be the case if either the convention’s terms are weakened or if the “Canal Istanbul” project proceeds — risks dragging the region into conflicts and wars reminiscent of the great-power rivalries of old.

A recent Russian commentary, as cited in Al-Monitor, is sobering: it says that, in the absence of the Montreux Convention, “…the situation in the straits will return to 1913. At the time, the Ottoman Empire could, at its discretion, let or not let any foreign ship into the Black Sea. This was one of the reasons for the numerous Russian-Turkish wars …” It is a thinly veiled reminder of the legacy of lost wars to Russia in recent Ottoman times as well as to how the Ottoman Empire was dragged into World War I after two German warships (reflagged under the Ottoman flag) sailed through the straits to bomb Sevastopol on the side of the Entente powers. The end of WWI saw the dissolution of the Ottoman Empire and its replacement by the Turkish republic, which did not recover its sovereignty over the Turkish straits until the adoption of the Montreux Convention. This history continues to bear on Turkish institutional memory and explains its established policy of jealously guarding the convention from any breaches.

Hence, when developing policies to deter mounting Russian security challenges, it will be important to bear in mind that circumventing the Montreux Convention risks aggravating the security and stability of the Black Sea. It remains, against all odds and challenges, an instrument that continues to serve the interests of its signatories as well as the broader international community. It would be self-defeating if transatlantic allies where to push back on Russian challenges to basic norms of international relations, such as the inviolability of territorial borders, by undermining a rare example of such an order that is entering its 86th year. This would especially be the case when a U.S. president is, rightfully, advocating a return to a rules-based international order. Lastly, it is as important that Turkey, as the legal guardian of the Montreux Convention, refrains from adopting policies that throw the future of the convention into doubt.

IMAGE: Ships from countries participating in exercise Sea Breeze 2018 sail in formation during a photo exercise in the Black Sea, July 13, 2018. Sea Breeze is a U.S. and Ukraine co-hosted multinational maritime exercise held annually in the Black Sea and is designed to enhance interoperability of participating nations and strengthen maritime security within the region. (U.S. Navy photo by Mass Communication Specialist 2nd Class Ford Williams/Released via Wikimedia Commons)