The Black Sea has played an overlooked part in Russia’s war on Ukraine, from the annexation of Crimea in 2014 to the full-scale assault on Ukraine launched a year ago. While most news coverage and analysis in the past year has, perhaps understandably, examined the more visible combat on land, Black Sea naval operations remain an important operational domain that deserve greater attention. The United States has no naval vessels in the Black Sea currently, but there are some calls for a greater U.S presence there. Congress recently introduced bipartisan legislation urging the Biden administration to develop a comprehensive Black Sea Strategy.

So the time is ripe to reassess the U.S. and NATO approach in the Black Sea, as panels at two symposiums are doing this week at the University of Virginia School of Law and the Ohio State University Moritz College of Law. In this article, I’ll follow up on my Just Security piece a year ago on the role of the Black Sea and the Montreux Convention in the Russia-Ukraine War. This installment will explore recent military operations in the Black Sea; how legal interpretations and applications are developing in something I would call the “Law of the Black Sea;” Turkey’s outsized role in the Russia-Ukraine conflict as of the Turkish Straits; and the way ahead for military operations in the Black Sea as the Russia-Ukraine conflict enters its second year of full-scale fighting.

Military Operations in the Black Sea 

Traditionally, naval operations in wartime encompass what U.S. Naval Academy Professor B.J. Armstrong has labelled the “Three B’s” — bombardment from sea, blockade, and “boots on the ground” via amphibious operations.  In the past year, Russia has employed “the Three B’s” with varying fervor and efficacy.  Tragically, Ukraine lacks naval power projection in the Black Sea due to Russia’s illegal seizure of Crimea and its key port, Sevastopol, where it had been leasing a naval base from Ukraine. Following this annexation, Ukraine lost 75 percent of its naval power overnight, and its naval forces centered on Odessa after 2014.

Despite these losses, Ukrainian forces have “punched above their weight” in the Black Sea. They sunk the Russian flag vessel Moskva, employed naval drones to damage Russian ships in Sevastopol, damaged the Kerch Strait Bridge that Russia built after 2014 to connect the Sea of Azov and the Black Sea, and reclaimed Snake Island, a key island that could have served as a launching point for an amphibious assault on Ukraine. Due to these successes, Russian naval forces have been somewhat chastened and have pulled away from a full-throated naval engagement strategy. But for how long? 

The “Law of the Black Sea” 

Maritime operations in the Black Sea are largely governed by the U.N. Convention on the Law of the Sea (UNCLOS), customary international law, and the 1936 Montreux Convention on the Turkish Straits.

Just as all roads lead to Rome, all maritime access to the Black Sea passes through the Turkish Straits. Article 35 of UNCLOS carves out a special provision for “long-standing international conventions in force . . related to straits.” This means that the Montreux Convention’s more restrictive provisions governing passage through the Turkish Straits apply to vessels entering and exiting the Black Sea. Because Montreux was negotiated more than 85 years ago, it can be a bit tricky to apply its technical provisions to modern warships.

Once inside the Black Sea, key UNCLOS provisions — such as the right to innocent passage — apply to naval forces that are not belligerents in the armed conflict. For Russia and Ukraine — belligerents in an international armed conflict — international humanitarian law and principles of military necessity, distinction, humanity, and proportionality continue to apply at sea, just as they do on land.

While UNCLOS applies to peacetime maritime operations, Montreux has provisions that apply in peace and war. What’s more, Montreux is unique in international law in that it explicitly favors the six “Black Sea powers” (Russia, Ukraine, Turkey, Romania, Georgia, Bulgaria). It discriminates against “non-Black Sea powers” (the United States and everyone else). Montreux places greater limitations on the size of the ships that non-Black Sea powers are allowed to bring into the Black Sea while limiting the total amount of time each ship can stay in the Black Sea before it must exit (21 days). Critically, three of the six Black Sea powers –Turkey, Romania, and Bulgaria — are NATO allies.

While the United States is not a party to the Montreux Convention, it abides by its restrictions as a legal matter. It may also be good foreign policy: Turkey is a key NATO ally and it views Montreux as sacrosanct. Nevertheless, there is some daylight emerging between the United States and Turkey’s approach in the Black Sea, and the United States should not give Turkey a blank check on all matters of Montreux’s interpretation.

Turkey possesses special authorities in interpreting the Montreux Convention’s provisions, playing a key role in regulating warship traffic to and from the Black Sea. At the beginning of the escalated conflict last year, President Volodymyr Zelenskyy of Ukraine requested that Turkey close the Straits. Turkey complied, closing the Turkish Straits to all military vessels. Turkey’s interpretation and application of the Montreux Convention has played a key role in deescalating tensions in the Black Sea. But its interpretation has caused a bit of head-scratching, particularly as the closure of the Turkish Straits to all warships must be premised on Turkey herself being threatened with war.  This position is increasingly untenable.

Implications for the Current Conflict and Beyond 

It remains unclear whether Turkey invoked Article 19 or Article 21 of the Montreux Convention when it closed the Straits to all military vessels last year. The Montreux Convention has provisions limiting Turkish Straits access for vessels of war belonging to belligerent powers (Ukraine and Russia) when Turkey is not at war (Article 19). Article 19 states that “in time of war, Turkey not being belligerent, warships shall enjoy complete freedom of transit and navigation through the Straits” consistent with earlier conditions.   When Turkey “considers herself to be threatened with imminent danger of war” (Article 21), Turkey has discretion to regulate the passage of all warships from belligerent and non-belligerent powers (Article 21).  The upshot:  Turkey appears to be applying Article 21’s more capacious restrictions without invoking Article 21 publicly.

Indeed, Turkey’s current closure goes well beyond Article 19. In February 2022, the Turkish Foreign Minister stated that “the situation in Ukraine has transformed into a war” and Turkey “will implement all articles of Montreux transparently.” Further, Turkish Foreign Minister Mevlüt Çavuşoğlu warned that no states should transit their warships through the Straits. Turkey’s invocation of Montreux’s wartime provisions has played a de-escalatory role, prohibiting Russian warships from the Baltics or elsewhere from entering the Black Sea.

But has Turkey been fully transparent in its Montreux interpretation? Article 19 only prevents Ukrainian and Russian vessels from outside the Black Sea from entering the Black Sea (unless they are returning to their home base). This interpretive disconnect was highlighted by the U.S. Naval War College’s Professor Pete Pedrozo earlier this year.   Since Turkey’s closure of the straits, no NATO vessels have transited the Black Sea, but Russian civilian merchant vessels carrying logistics and supplies to the Russian military have purportedly been allowed to transit the Straits. Analyst Yörük Işık of the Middle East Institute reported that Russia, during its military campaign in Syria, actually bought Turkish civilian vessels, reflagged them, and used them to resupply its war effort there.

This interpretive disconnect has implications for the current conflict and beyond. After all, Turkey’s invocation of Montreux’s wartime provisions marked just the second time this had ever occurred since 1936. Turkey’s opacity surrounding the legal contours of its invocation bolsters Turkey’s status as an intermediary in the conflict.

Can Turkey objectively claim that the country is threatened with war one year later? This claim would serve as the only legal basis for Turkey to block the passage of all warships through the Turkish Straits.

One year into the conflict, the United States and its NATO allies deserve more transparency from Turkey, particularly as a clear Article 19 invocation would permit NATO maritime powers to transit the Straits while prohibiting Russian vessels from doing so.  Whether this is a wise policy for the United States and NATO to pursue is an important question for the Alliance to consider, but it is one that should be disentangled from the legal authority to transit.

Additional questions remain. Is Russian reliance on civilian merchant vessels as naval auxiliaries exploiting a gap in the Montreux Convention, as some have argued? Could NATO minesweepers be allowed to transit the Turkish Straits in an effort to clear sea lanes? What about river patrol vessels pledged by the Biden administration or future maritime assets — could they transit the Straits or would naval vessels have to be shipped by land? These questions demand answers and require greater specificity from the Turkish government.

The Way Ahead in the Black Sea 

Turkish President Recep Tayyip Erdoğan is currently suffering from political fallout related to a devastating earthquake that has tragically killed tens of thousands of people in Turkey, in addition to almost 3,700 in Syria. It is unlikely that he will make a major policy decision governing Turkey’s interpretation of the Montreux Convention in the short term. Still, additional clarity is needed soon, particularly as the threat of naval mining increases and the U.N.-brokered Ukrainian grain shipments initiative expires in one month.  By one measure, Ukrainian grain exports have fallen by almost half since the war began and overall GDP is down by more than a third. How long will western economies have the appetite to prop up a flagging Ukrainian economy?

Russian access to the Black Sea is of great importance for Putin’s outsized ambitions, as acquiring key ports will ensure Russian access to the Mediterranean and beyond. Witness Putin’s annexation of Crimea, the location of the key naval port of Sevastopol, and control of the Kerch Strait. Putin signaled his interest in cutting off Ukraine from the Black Sea when he attacked another key port city, Odessa, at the beginning of the war. Cutting off southern Ukraine from the Black Sea and capturing the key Ukrainian port of Odessa would give Russia dominance of the Black Sea for generations.

While some U.S. senators have called on the U.S. Navy to press Turkey to allow American destroyers into the Black Sea, that seems unlikely to occur. A compromise may be to allow a NATO minesweeper to transit the Black Sea to sweep mines along the Danube River. Before transit, Montreux requires 15 days of transit notice to Turkey, ample time for U.S. and Turkish diplomats to hash out potential interpretive differences. The naval mining threat is real, and failure to proactively clear mines could wreak havoc on the Black Sea for years. A Romanian vessel struck a mine five months ago, and grain shipments from Ukraine to the rest of the world remain exposed to naval mines. Eliminating that threat would help safeguard the Black Sea and help set the conditions for peaceful maritime operations without provoking a Russian response.


As the war grinds on, more attention should be played to the Black Sea and Turkey’s outsized role in interpreting the Montreux Convention. As noted above, two symposiums are being held at the University of Virginia School of Law and the Ohio State University Moritz College of Law this week to mark the one-year anniversary of this brutal armed conflict. Organized by the Virginia Journal of International Law and Ohio State Law Review, respectively, they include panels related to these Black Sea issues (in which I will be taking part with others, including fellow Just Security contributors Professors Dakota Rudesill and Kristen Eichensehr).

A Black Sea power, Georgia, offers a cautionary tale and a possible blueprint that Putin is cynically trying to follow. Russia invaded Georgia in August 2008 and captured two of its regions, South Ossetia and Abkhazia, just months after NATO made a deliberately vague pledge of membership to Ukraine and Georgia, without offering a timeframe or the usual first step, a membership action plan. Half of Georgia’s Black Sea coastline in Abkhazia  is now contested territory and no longer under Georgian control. This coastline loss — coinciding with a range of political upheaval — has left Georgia a Black Sea power in name only.

While the Ukrainians have fought valiantly with their limited naval forces, the naval order of battle very much favors the Russians in the long term. The Russian Navy’s relative dominance is poised to take on growing importance as the war enters its second year. Some commentators have argued that the land campaign failure will give way to a “bastion” strategy for the Russian Navy to attack Ukraine from relatively safe coastal areas. The United States and its NATO allies ignore this reality — and Russia’s distinct advantage in the maritime domain — at their peril.

IMAGE: An aerial view shows ships at the anchorage area of the Bosphorus southern entrance in Istanbul, on October 12, 2022. A grain deal between Russia and Ukraine established safe corridors along which Ukrainian ships can come in and out of three designated Black Sea ports in and around Odessa and through the Turkish Straits.  (Photo by YASIN AKGUL/AFP via Getty Images)