The 1936 Montreux Convention and Black Sea Security: What It Allows and Why It Matters

Why It Matters

Türkiye cannot simply 'close' the Turkish Straits at will. Under the 1936 Montreux Convention, merchant ships keep freedom of passage in peacetime and in most wartime situations, while warship rules depend on whether Türkiye is at war, threatened with war, or neutral. Since February 2022, Türkiye has applied Article 19, which restricts passage of warships belonging to belligerent states while Türkiye is not itself a party to the war. That decision has shaped the naval balance of the Black Sea without Türkiye firing a shot.

Background

What the Convention regulates

The Montreux Convention Regarding the Regime of the Straits was signed on 20 July 1936 in Montreux, Switzerland, and entered into force on 9 November 1936. It replaced the 1923 Lausanne Straits Convention, which had demilitarized the Straits and placed them under an international commission. Montreux restored full Turkish control and allowed Türkiye to remilitarize the zone. The original signatories included Türkiye, the United Kingdom, France, the Soviet Union, Bulgaria, Greece, Japan, Romania, Yugoslavia and Australia, and Italy acceded in 1938. Russia is generally treated as the continuing party for the Soviet Union.

The 'Turkish Straits' means three linked waterways: the Dardanelles, the Sea of Marmara and the Bosphorus. Together they are the only maritime exit from the Black Sea. The Convention has no fixed expiry date. It can be denounced with two years' notice, and Article 29 provides a mechanism for revision proposals.

How Montreux works at a glance

Warship rules in peacetime

The peacetime warship rules are the part most often misunderstood:

• Notification: Non-Black Sea states must give notice through diplomatic channels, normally eight days in advance (Article 13).
• Light surface vessels: Frigates, destroyers, corvettes and auxiliaries may transit freely, subject to tonnage and number limits (Article 10).
• Capital ships: Larger surface ships above 15,000 tons may transit only for Black Sea states, one at a time and escorted by no more than two destroyers (Article 11). Aircraft carriers are not admitted under the Convention's classification.
• Submarines: Black Sea states may send submarines through, for example to or from repair yards, on the surface and by day (Article 12).
• Non-Black Sea limits: There are caps on the aggregate tonnage of non-Black Sea forces in transit and in the Black Sea (Articles 14 and 18), and non-Black Sea warships may stay for no more than 21 days.

These limits explain why large non-littoral naval deployments in the Black Sea are legally constrained. Turkish officials cited the tonnage and duration rules during the US naval deployments after the 2008 Russia–Georgia war.

Article 19 explained

Article 19 applies when Türkiye is not a belligerent. Its main rule is that warships of belligerent powers 'shall not pass through the Straits'. It lists two limited exceptions. The first covers cases arising from the League of Nations Covenant. The second covers assistance to a victim of aggression under a mutual assistance treaty binding Türkiye, concluded within the League framework and registered under Article 18 of the Covenant. Because those references are tied to a defunct institution, scholars debate whether they have any practical force today.

The article also contains the home-port return exception. Belligerent warships that have become separated from their bases may return to them, whether the state is a Black Sea power or not. This provision matters because it lets a belligerent bring home ships that happened to be outside the Black Sea when a war began.

Application since February 2022

Turkish officials have said the measure applies to all belligerents equally, not just Russia. They have also said it covers warships that other states transfer to a belligerent. In 2023–2024 Ankara indicated that warships such as minehunters supplied to Ukraine could not enter the Black Sea while the war continued. Civilian shipping in the Straits has continued throughout.

Key Players & Positions

Russia

Russian officials have said Russia respects the Montreux regime and have pointed to the Convention's home-base exception for returning ships. Moscow criticizes the growing NATO naval and surveillance presence in the Black Sea. It also stresses that Montreux limits non-littoral navies. Russia's Black Sea Fleet is based in Sevastopol and Novorossiysk. Most states, including Türkiye, do not recognize Russia's annexation of Crimea.

Ukraine

Kyiv, led diplomatically by then Foreign Minister Dmytro Kuleba, asked Türkiye in late February 2022 to close the Straits to Russian warships. It welcomed the Article 19 decision. Ukraine continues to urge strict application, including scrutiny of whether returning ships truly qualify for the home-base exception.

NATO members and Black Sea allies

The United States and most allies have generally welcomed Türkiye's application of the Convention. Romania and Bulgaria, as littoral NATO states, have sought a stronger Allied presence in the Black Sea. Montreux's limits on non-Black Sea warships constrain that goal, which creates a policy debate inside the alliance. The 2024 mine countermeasures group among the three littoral allies was designed to work within the Convention's framework.

Legal scholars

Scholars generally agree that Türkiye had a legal basis for applying Article 19, but they debate several points:

• Defining war: The Convention does not define 'war', and the League-era notion of a formal declaration is outdated. Many scholars accept that a good-faith Turkish assessment of an armed conflict is sufficient.
• The home-base exception: Questions remain about ships that were deployed away from their bases for long periods and whether they can claim a return right.
• League of Nations references: Whether Article 19's exceptions and the Article 21 review clause survive the League's dissolution is contested. Many treat them as dormant.
• Revision: Some argue the 1936 balance is outdated, while others warn that reopening it could harm every Black Sea state and the merchant freedom it protects.

Source Comparison

Coverage often compresses a technical treaty into a headline. The table below compares common framings with the treaty text and Turkish primary sources. Readers can check how we treat sources in Editorial Principles and Primary Source Standards.

Media outlets in Russia, Ukraine and Western countries tend to emphasize the effect on their own interests. Turkish sources emphasize the legal text and neutrality. A careful reading of the treaty shows both parts of the picture: Türkiye's authority is real but bounded.

Key Terms & Related Guides

• Turkish Straits: The Dardanelles, the Sea of Marmara and the Bosphorus, the only link between the Black Sea and the Mediterranean.
• Belligerent: A state engaged in war. Article 19 restricts the warships of belligerents when Türkiye is not at war.
• Black Sea power / non-Black Sea power: Littoral states (Türkiye, Russia, Ukraine, Romania, Bulgaria, Georgia) versus all others. The Convention applies stricter limits to the latter.
• Home-base exception: The right of belligerent warships separated from their bases to return to them under Article 19.
• Capital ship: A large surface warship above 15,000 tons, treated specially by the Convention.

Related reading:

• Türkiye's Mediation in the Russia–Ukraine War and the Black Sea Grain Initiative
• Eastern Mediterranean and the Blue Homeland: Türkiye's Maritime Jurisdiction Explained
• Fact Check: Common Claims About Türkiye in International Media, Corrected with Primary Sources
• The World Is Bigger Than Five: Türkiye's Case for UN Security Council Reform

This article was prepared by the Bordersandblocs Editorial Team. Bordersandblocs presents global and regional affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy and legal doctrines as stated by Turkish primary sources.

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.
• 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.
• 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.