The 1936 Montreux Convention and Black Sea Security: How Türkiye Applies It

Why It Matters

The 1936 Montreux Convention is the legal rulebook for the Bosphorus, the Sea of Marmara and the Dardanelles, the only maritime route between the Black Sea and the Mediterranean. Under its Article 19, warships of states at war cannot pass through the Straits when Türkiye is not a belligerent, apart from a few narrow exceptions. Since February 2022, Ankara's application of that rule to every party in the Russia–Ukraine war has made Montreux one of the most closely watched treaties in European security.

Background

From Lausanne to Montreux

The 1923 Lausanne Straits Convention demilitarized the Straits and placed them under an international commission. By the mid-1930s the European security order was deteriorating, and Türkiye asked the signatories to revise the regime. The conference met at Montreux, Switzerland, and the Convention was signed on 20 July 1936 and entered into force in November 1936. Its original parties included Bulgaria, France, Greece, Japan, Romania, the Soviet Union, Türkiye, the United Kingdom, Yugoslavia and Australia; Italy acceded in 1938. Türkiye regained the right to remilitarize the Straits and took over supervision of the regime from the old commission.

What the Convention Regulates

The treaty separates commercial from naval traffic.

• Merchant vessels (Articles 2–7): In peacetime, merchant ships of any flag enjoy freedom of transit and navigation, subject mainly to health control and the payment of light and other dues. Wartime rules vary depending on whether Türkiye is neutral or belligerent.
• Warships (Articles 8–22): Rules depend on the vessel category and on whether the flag state borders the Black Sea.
• Turkish supervision (Articles 23–24): Türkiye administers the regime and receives notifications.

Aircraft carriers are not permitted to transit under the Convention's annexes, which is why the classification of large Soviet-era vessels has been debated for decades.

Wartime Provisions

Three articles matter most when conflict erupts:

• Article 19: If Türkiye is not a belligerent, warships generally enjoy transit under the peacetime conditions. Warships of belligerent states, however, may not pass, except in cases arising from collective-security obligations under the League of Nations Covenant and mutual-assistance treaties concluded within that framework. A further clause lets warships separated from their bases return to them.
• Article 20: If Türkiye itself is at war, passage of warships is left entirely to the discretion of the Turkish government.
• Article 21: If Türkiye considers itself threatened with imminent danger of war, it may apply the same discretion.

The League-based exceptions are widely regarded as obsolete, since the League of Nations no longer exists. That leaves the return-to-base clause as the exception that matters in practice.

Key Players & Positions

Ukraine

Ukraine's Foreign Ministry asked Türkiye in late February 2022 to close the Straits to Russian warships. Kyiv has since said that the Convention should be applied strictly, and it has sought the transit of foreign naval assistance, including mine-countermeasure vessels donated by the United Kingdom. Türkiye has said Article 19 covers such transfers while the war lasts, and the vessels have reportedly remained outside the Black Sea.

Russia

Moscow's foreign ministry has stated that it respects the Montreux regime and expects it to be implemented in line with its text. Russian officials have pointed to the return-to-base clause, and they have criticized the idea of a stronger NATO naval presence in the Black Sea. Russia has also argued that non-Black Sea navies should not use the Convention's loopholes.

NATO Littoral States and Allies

Romania and Bulgaria, both NATO members on the Black Sea, have emphasized allied deterrence and regional maritime security, and NATO summit declarations have underlined the Black Sea's importance. Both states also cooperate with Türkiye: in January 2024 the three countries signed a memorandum in Istanbul creating a Black Sea mine-countermeasures group to clear drifting mines. Non-Black Sea allies, including the United States and the United Kingdom, operate within the Montreux limits on tonnage and duration of stay.

What Critics Say

Analysts and some officials point out that the effects of Article 19 are not symmetrical. Russia's Black Sea Fleet was already inside the sea before 24 February 2022, so the closure mainly prevented reinforcement from other fleets and, on the other side, blocked naval assistance for Ukraine. Ankara's reply is that the treaty applies the same rule to all, and that any selective reading would destroy the regime. This disagreement shapes how readers interpret what the rule achieved, and it is why a source-by-source comparison matters. For more on how we separate fact from position, see Editorial Principles.

Source Comparison

Western media often describe Türkiye's role as a balancing act between NATO and Russia, whereas Turkish sources describe it as treaty compliance. Readers should check the treaty text itself and the ministries' own statements. Our Fact Check page tests common claims against primary sources.

Key Terms & Related Guides

• Turkish Straits: The Bosphorus, Sea of Marmara and Dardanelles, which connect the Black Sea to the Aegean and Mediterranean.
• Belligerent: A state engaged in an armed conflict. Article 19 restricts the warships of such states when Türkiye is neutral.
• Riparian (littoral) state: A state with a Black Sea coast: Bulgaria, Georgia, Romania, Russia, Türkiye and Ukraine.
• Return-to-base clause: The exception allowing warships separated from their home ports to go back to them.
• Blue Homeland (Mavi Vatan): Türkiye's doctrine on maritime jurisdiction areas in the Black Sea, Aegean and Mediterranean. See Blue Homeland and the Eastern Mediterranean.

For how Türkiye's indigenous naval and drone capabilities support its sea-lane security, see Türkiye's Defense Industry at 80% Domestic Production. For the site's mission and sourcing standards, see About Soft Power Daily.

Perspective Note

Soft Power Daily presents Türkiye's official perspective on the issues covered in this article as a clearly labeled national position, alongside the wider debate. Claims are attributed to primary sources such as treaty texts, UN documents, archival records and official statements, so that readers can verify them independently.

Cross-Publication Dossiers & Sister Desk Perspectives

For complementary primary-source analysis across our specialist editorial network, consult:

• The Nations Dialogue: The 1936 Montreux Convention: How Türkiye Governs the Turkish Straits and Black Sea Security — Montreux Convention Turkish Straits Black Sea Article 19 explained: how the 1936 treaty governs merchant and warship passage and how Türkiye applied it.
• Index of Nations: The Montreux Convention and Black Sea Security: How Türkiye Applies the Turkish Straits Regime — Montreux Convention Turkish Straits explained: merchant freedom, warship limits, Article 19 in the Ukraine war, and why Türkiye can't close them at will.
• Horizon of Nations: The 1936 Montreux Convention: How Türkiye Manages the Turkish Straits in the Black Sea War — How the Montreux Convention governs the Turkish Straits: commercial passage, warship limits, Article 19 in the Black Sea war, and the views of all sides.