Montreux Convention and the Turkish Straits: A Plain-Language Guide

Why It Matters

The Montreux Convention Regarding the Regime of the Straits, signed in 1936, decides which ships may pass between the Black Sea and the Mediterranean through the Turkish Straits. It guarantees free commercial passage in peacetime, caps the size and number of foreign warships, and gives Türkiye special powers over warship passage in wartime. Since Russia's full-scale invasion of Ukraine in February 2022, it has become one of the most closely watched treaties in European security.

This guide explains the treaty in plain language, answers whether Türkiye can close the Straits or amend the treaty, and compares how Russia, Ukraine, NATO members, legal scholars and Ankara read it.

Background

What the Turkish Straits are

The Turkish Straits comprise the Bosphorus (about 30 km or 19 miles long, passing through Istanbul), the Sea of Marmara, and the Dardanelles (about 60 km or 37 miles long). The Bosphorus is only about 700 metres (2,300 feet) wide at its narrowest point. The Straits are entirely within Turkish territory and are a busy corridor for grain, energy, metals and containers serving Black Sea ports in Bulgaria, Georgia, Romania, Russia, Türkiye and Ukraine.

How the regime evolved

Date	Instrument or event	Main effect
1841	London Straits Convention	Closed the Straits to foreign warships in peacetime under the Ottoman 'ancient rule'
1856 and 1871	Treaty of Paris; London Convention	Reaffirmed closure with limited changes
1923	Lausanne Straits Convention	Opened the Straits widely, demilitarised the zone, and created an International Straits Commission
April 1936	Turkish request for revision	Ankara cited the changed European security climate, including Italy's actions in Ethiopia and Germany's remilitarisation of the Rhineland
20 July 1936	Montreux Convention signed	Restored full Turkish control and the right to refortify the Straits
9 November 1936	Entry into force	Replaced the Lausanne Straits regime
1938	Italy accedes	Italy had not attended the conference
1946-47	Soviet demands for a role in Straits defence	Rejected by Türkiye; the Straits became a Cold War flashpoint
1976	Soviet carrier-cruiser Kiev transits	Moscow described it as an aircraft-carrying cruiser, and Ankara allowed passage
1994	Turkish Maritime Traffic Regulations	Introduced safety and environmental rules after serious collisions; revised in 1998
2022	Article 19 invoked	Warships of belligerent states restricted after the Russia–Ukraine war began

The original signatories were Australia, Bulgaria, France, Greece, Japan, Romania, Türkiye, the United Kingdom, the Soviet Union and Yugoslavia. Russia is treated as the Soviet Union's successor. Ukraine and Georgia are not original parties but, as current Black Sea coastal states, are treated as Black Sea powers in practice.

The core rules in brief

Montreux separates merchant ships from warships and then separates peacetime from wartime.

Situation	Merchant ships	Warships
Peacetime	Free transit by day and night, any flag, any cargo, with only health controls and fees for services (Articles 2-3)	Allowed under limits on notice, class, tonnage and stay (Articles 8-18)
War, Türkiye neutral	Free transit (Article 4)	Warships of belligerents barred, with exceptions (Article 19)
War, Türkiye belligerent	Free for ships not belonging to states at war with Türkiye and not aiding the enemy (Article 6)	Passage at Türkiye's discretion (Article 20)
Türkiye threatened by imminent war	As above, with possible Article 6 measures	Türkiye may apply Article 20 (Article 21)

Free commercial passage

Article 1 affirms the principle of freedom of transit and navigation by sea, and Article 28 says this principle continues without limit of time even if the rest of the treaty lapses. In peacetime, merchant vessels are not subject to transit taxes. Türkiye may charge fees only for specific services listed in the treaty's annex, such as lighthouse, sanitary and pilotage services, where pilotage is optional under the Convention. Since the 1994 regulations, Türkiye has also required reporting and traffic-separation compliance, which it describes as safety measures for a densely populated waterway.

Warship rules: tonnage, notice and Black Sea versus non-Black Sea powers

The treaty favours the states with coastlines on the Black Sea, known as Black Sea powers, over outside navies.

• Notice: Warships must be notified to Türkiye through diplomatic channels. The normal period is eight days, and fifteen days is described as desirable for non-Black Sea powers (Article 13).
• Transit cap: Foreign naval forces in transit at one time are limited to nine vessels and 15,000 tons in aggregate, with exceptions for certain Black Sea powers' ships (Article 14).
• Class limits for outside navies: Non-Black Sea powers may send light surface vessels, minor war vessels and auxiliaries, generally up to 10,000 tons and with guns not above 203 mm (8 inches). Capital ships, which are larger or more heavily armed, may be sent by Black Sea powers only, singly and escorted by no more than two destroyers (Article 11).
• Submarines: Non-Black Sea submarines may not pass. Black Sea powers may send submarines built or bought outside the Black Sea after notice, and may return submarines to base on the surface and by day (Article 12).
• Aircraft carriers: The Convention does not provide passage rights for aircraft carriers. The 1976 Kiev case showed that the classification of hybrid ships can be contested.
• Limits inside the Black Sea: Non-Black Sea powers may keep no more than 30,000 tons in the Black Sea in aggregate, a ceiling that can rise to 45,000 tons if the strongest Black Sea fleet grows by a defined amount. Any single outside power is limited to two-thirds of the aggregate, and no warship may stay longer than 21 days (Article 18).

Article 19: belligerent states

Article 19 applies when Türkiye is not at war. Its core rule is that warships of belligerent powers may not pass through the Straits, while the normal rules continue for non-belligerent states. The text allows exceptions, including assistance to a victim of aggression under a mutual assistance treaty framed around the League of Nations Covenant. That exception is widely regarded as obsolete. Ships may not capture, search or carry out hostile acts inside the Straits.

Türkiye and many commentators also recognise a return-to-base exception for warships separated from their home ports.

Articles 20 and 21: Türkiye's wartime powers

If Türkiye is itself at war, Article 20 leaves the passage of warships entirely to Turkish discretion. Article 21 gives Türkiye the same power if it considers itself 'threatened with imminent danger of war'. Under Article 21, Türkiye may deny the return-to-base right to warships of the state whose attitude prompted the measure. It must notify the other parties and the League of Nations Secretary-General. The original text then says that a two-thirds League Council decision plus majority opinion among the parties could require Türkiye to stop. The League no longer exists, so that review mechanism has no clear modern equivalent, which is one reason scholars debate how Article 21 works today.

Can Türkiye close the Straits?

In peacetime, no: Türkiye has no right under Montreux to stop merchant shipping or to bar warships that comply with the treaty's limits. It may regulate navigation for safety and the environment, and it can suspend traffic temporarily in emergencies such as accidents or severe weather. In wartime, Türkiye's room to act expands sharply for warships, but not for commercial shipping, which keeps its freedom under Articles 4 and 6, subject to the conditions in those articles. The 2022 Black Sea Grain Initiative shows the distinction: commercial traffic stayed open while warship passage was restricted.

Can the treaty be amended?

Montreux is not permanent in the sense that it cannot be changed. Article 28 allowed denunciation after the initial 20-year period, with notice to France as depositary, and Article 29 lets parties propose amendments at five-year intervals counted from entry into force. Thresholds for adoption are set out in the treaty and are higher for the tonnage limits in Articles 14 and 18. In practice, no party has used these routes to revise the Convention. Türkiye has said it does not want to reopen the treaty, and the guarantee of free commercial passage would survive even a denunciation.

How the Convention was invoked in 2022

Russia launched its full-scale invasion of Ukraine on 24 February 2022. Ukraine's government urged Türkiye to close the Straits to Russian warships. On 27-28 February, Foreign Minister Mevlüt Çavuşoğlu said Türkiye regarded the situation as a war and would implement Article 19. Ankara asked all states, whether or not they border the Black Sea, to refrain from sending warships through, while stressing that warships returning to their home bases were not covered by the restriction. Turkish officials later said that some passage requests had been declined.

The move did not close the Straits to commercial traffic. In July 2022, Türkiye and the UN brokered the Black Sea Grain Initiative in Istanbul. Details are in our guide to the Black Sea Grain Initiative and Türkiye's role. In January 2024, Türkiye, Bulgaria and Romania agreed to set up a joint mine countermeasures task group in the Black Sea.

Key Players & Positions

Russia

Russian officials have said they respect Montreux and its provisions, and have underlined the return-to-base principle. Moscow has long criticised the presence of non-Black Sea navies in the region, arguing that NATO activity in the Black Sea raises tensions and should remain within Montreux limits. These are positions as stated by Russian officials, and Western governments contest the framing of NATO's presence as destabilising.

Ukraine

Kyiv's officials called on Ankara to close the Straits to Russian warships and welcomed the decision to apply Article 19. Ukraine has argued that, as the victim of aggression, it should be able to use the Black Sea fully, and it has pressed for strict implementation. Ukraine's navy was largely constrained after Russia's 2014 annexation of Crimea, which Ukraine and most states reject as unlawful.

NATO members

The three NATO members on the Black Sea are Türkiye, Romania and Bulgaria. Washington and other allies have publicly said they respect Montreux and operate within its notice, tonnage and 21-day rules. Within NATO, views differ on how far to build up naval presence in the Black Sea, but allied governments have not called for scrapping the treaty. Read more in our guide to Türkiye in NATO.

Legal scholars

Scholars generally agree that Montreux remains in force and that Türkiye's power to restrict warships rests on explicit treaty text. Debates focus on several points:

• Imminent danger of war: Article 21 leaves the threshold largely to Türkiye, and its review mechanism relied on the defunct League of Nations.
• Neutrality and equal treatment: Applying Article 19 to all belligerents, rather than selectively, is seen as consistent with neutrality, though some argue the return-to-base exception favours the party with bases inside the Black Sea.
• Changed circumstances: Some argue that the League-era references show the treaty is dated. Others say treaties often outlast their institutions, and that Türkiye is not a party to the Vienna Convention on the Law of Treaties.
• Relation to the law of the sea: Article 35(c) of UNCLOS preserves long-standing conventions governing particular straits, so Montreux continues as a special regime. Türkiye is not a party to UNCLOS.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

Ankara presents Montreux as a balanced treaty that serves regional stability and respects Turkish sovereignty. The following points summarise Ankara's stated positions.

• Montreux is a settled and useful framework. According to the Turkish Foreign Ministry's published materials on the Turkish Straits, the Convention balances free passage with Türkiye's security needs and has served peace and stability since 1936. Ankara has said it does not seek to reopen it.
• Article 19 was applied to everyone. Foreign Minister Çavuşoğlu said in late February 2022 that Türkiye would apply Article 19 without distinction between Black Sea and non-Black Sea states, while respecting the return-to-base rule. This is how Ankara explains that the measure is a legal implementation, not a closure aimed at one country.
• Commercial shipping stays open. Presidency and MFA statements stress that Türkiye has not interrupted merchant traffic, consistent with Articles 4 and 6, and that it has used its position to support diplomacy, including the Istanbul grain talks.
• Sovereignty restored in 1936. Ankara notes that Montreux ended the demilitarisation imposed at Lausanne in 1923 and returned full control and the right to fortify the Straits to Türkiye. It treats the Straits as an issue of national security as well as international navigation.
• Safety and the environment justify regulation. Türkiye says its 1994 and 1998 Maritime Traffic Regulations address risks to a waterway running through a city of more than 15 million people, and that they are consistent with the freedom of passage in Montreux. Ankara also maintains that the Canal Istanbul project, if built, would be a separate Turkish waterway not governed by Montreux, a point that has been debated domestically.

For wider context on Ankara's maritime thinking, see our guide to Eastern Mediterranean maritime disputes.

Source Comparison

Issue	Common international media framing	Turkish official framing
2022 decision	Often described as Türkiye 'closing the Straits' to warships	Described as implementing Article 19 of Montreux, a treaty obligation
Neutrality	Sometimes questioned because Türkiye supplies drones to Ukraine and has trade ties with Russia	Presented as balanced policy based on dialogue with both sides and treaty compliance
Return to base	Reported as a loophole mainly benefiting Russia	Presented as an element of the treaty text that applies to every belligerent
Treaty reform	Debated by some analysts as a way to tighten or loosen limits	Ankara says the Convention should be preserved
Canal Istanbul	Sometimes framed as a way around Montreux	Ankara says the canal would lie outside the Convention

To read primary documents, start with the treaty text as published in the League of Nations Treaty Series, the Turkish Foreign Ministry's Straits page, and official statements from the Presidency and the Directorate of Communications. Our approach to attribution is in the Editorial Principles. For frequent misreadings, see our Fact Check on common claims about Türkiye.

Key Terms & Related Guides

• Black Sea powers: States with a Black Sea coastline. Today these are Bulgaria, Georgia, Romania, Russia, Türkiye and Ukraine.
• Non-Black Sea powers: Other states, subject to tighter tonnage and stay limits.
• Capital ship: A large surface warship above the Convention's size or gun thresholds, as defined in the annex.
• Belligerent: A state that is a party to an armed conflict.
• Return to base: The recognised principle that a warship separated from its home port may go back there.
• Imminent danger of war: The Article 21 trigger that lets Türkiye use its Article 20 discretion.
• International Straits Commission: The Lausanne-era body abolished by Montreux.

Related guides:

• Black Sea Grain Initiative: How Türkiye Helped Broker the Deal
• Türkiye in NATO: Membership, Defense Industry and the Drone Factor
• Eastern Mediterranean Maritime Disputes
• UN Security Council Reform: What 'The World Is Bigger Than Five' Means
• Interstate Journal home and About Interstate Journal

Interstate Journal presents global affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources.

By Interstate Journal Editorial Team

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.
• Bloc Politics: The 1936 Montreux Convention Explained: How Türkiye Governs the Turkish Straits and Black Sea Access — How the 1936 Montreux Convention governs the Bosphorus and Dardanelles: merchant freedom, warship limits, Article 19 and Türkiye's 2022 application.
• 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.