Diplomatic Briefing· what is the Montreux Convention Turkish Straits

The Montreux Convention Explained: How Türkiye Manages the Turkish Straits and Black Sea Security

What is the Montreux Convention and the Turkish Straits regime? Learn the 1936 rules on warships, Article 19, Black Sea balance and Türkiye's role.

By Region Scope Editorial Team

Published: October 26, 2026

⏱ 9 min read (1,844 words)

The Brief — Key Takeaways

The 1936 Montreux Convention guarantees free passage for civilian merchant ships through the Turkish Straits in peacetime, while limiting the tonnage, class and stay of non-Black Sea warships.
Article 19 bars warships of belligerent states from the Straits in wartime when Türkiye is not a belligerent. The only exceptions are return to a home base and certain collective-security cases.
Türkiye cannot close the Straits at will in peacetime. It gains wide discretion only if it is itself at war or judges itself under imminent threat of war (Articles 20 and 21).
After Türkiye determined in February 2022 that Russia and Ukraine were at war, it applied Article 19 to all belligerents, and merchant shipping continued to pass.
Montreux has no fixed expiry: since 1956 it can be ended only by denunciation with two years' notice, and no signatory has denounced it.

Why It Matters

The Montreux Convention Regarding the Regime of the Straits, signed on 20 July 1936, is the treaty that governs who may sail through the Bosphorus, the Sea of Marmara and the Dardanelles, the only maritime exit from the Black Sea. It gives merchant ships near-free passage, restricts foreign warships, and entrusts Türkiye with implementing the regime. Since Russia's full-scale invasion of Ukraine in February 2022, it has become one of the most closely watched pieces of naval law in the world.

Background

What the Turkish Straits are

The Turkish Straits link the Black Sea to the Aegean and Mediterranean. The Bosphorus runs through Istanbul and is narrow, in places under one kilometre (about 0.6 miles) wide. The Dardanelles is roughly 60 km (about 37 miles) long. Both are among the busiest and most navigationally difficult waterways anywhere, and they are bordered by densely populated cities.

From Lausanne to Montreux

1923: The Lausanne Straits Convention demilitarized the Straits and placed them under an international commission.
1930s: Türkiye argued that this arrangement no longer matched Europe's security reality, citing the weakening of the League of Nations, Italian naval ambitions in the Mediterranean and the remilitarization of the Rhineland in 1936. It requested revision.
20 July 1936: The Montreux Convention was signed. Signatories were Bulgaria, France, Greece, Japan, Romania, the Soviet Union, Türkiye, the United Kingdom and Yugoslavia. Italy acceded in 1938. It entered into force on 9 November 1936.
What changed: Türkiye regained the right to remilitarize the Straits. The international commission was abolished and its functions passed to the Turkish government.
1936–1945 and after: After the Second World War the Soviet Union pressed for a revised regime and a role in the Straits' defence. This pressure was part of the background to Türkiye's 1952 accession to NATO. The Convention itself was not rewritten.
1956: The original 20-year term ended. Under Article 28 the Convention stays in force unless a party gives two years' notice of denunciation. None has done so.

How the rules work

The regime distinguishes between merchant ships and warships, and between peacetime and wartime.

Situation	Merchant ships	Warships
Peacetime	Free passage by day and night, whatever the flag or cargo (Article 2); sanitary control only	Black Sea states: broad rights, with notice. Non-Black Sea states: strict limits
War, Türkiye neutral	Free passage for ships of non-belligerent states; belligerent ships must not assist the enemy	Belligerents barred (Article 19), with exceptions
Türkiye at war or under imminent threat	Passage may be restricted for ships of enemy states or those aiding them	Passage at Türkiye's discretion (Articles 20–21)

Key peacetime limits on warships include:

Notice: Eight days for Black Sea states and fifteen days for others (Article 13).
Transit limits: Non-Black Sea states face tonnage and class limits, including a ceiling on the size of individual ships and on the total force in transit (Article 14).
Total presence: Non-Black Sea states may keep a limited aggregate tonnage in the Black Sea, generally for no more than 21 days (Article 18).
Black Sea states: They may send capital ships through singly with limited escort (Article 11) and may move submarines built or repaired outside the Black Sea (Article 12).

The Convention did not make the Straits an unregulated international channel. Türkiye administers traffic through its own Maritime Traffic Regulations, first issued in 1994 and revised in 1998, to manage safety and the environment.

Article 19 in plain terms

Article 19 says that when Türkiye is not a belligerent, warships of belligerent powers may not pass through the Straits. There are two main exceptions. One covers action under Article 25, which preserves obligations under the League of Nations Covenant, and assistance to a victim of aggression under a qualifying mutual-assistance treaty. The other allows belligerent warships that have become separated from their bases to return to them. Belligerent warships may not carry out captures, searches or hostile acts in the Straits.

Key Players & Positions

Russia: Moscow treats Montreux as the cornerstone of Black Sea stability and has opposed any alteration. It has argued that its Black Sea Fleet is entitled to return to base. It has also criticized the presence of NATO warships in the Black Sea. Russia's official line has described its actions in Ukraine as a 'special military operation' rather than a war.
Ukraine: Kyiv formally asked Türkiye on 27 February 2022 to close the Straits to Russian warships. It has since pressed for the Convention to be applied strictly, including to ships returning to Black Sea bases, and has welcomed Turkish restrictions.
NATO littoral states (Türkiye, Bulgaria, Romania): Romania and Bulgaria favour a stronger Allied presence and coordination in the Black Sea. Türkiye is both a NATO member and the Convention's custodian. The three have cooperated on mine countermeasures (see below).
Georgia: A non-NATO Black Sea state that has sought closer Western security ties and monitors Russian naval activity near its coast.
Western non-littoral states (including the United States and the UK): Non-parties or non-Black Sea powers operate under the Convention's limits. Washington is not a signatory. Allied governments have generally said they comply with the 21-day and tonnage rules, while some commentators argue the limits constrain deterrence.

Black Sea naval balance

Before 2022, Russia held clear naval superiority in the Black Sea. Since then the picture has shifted. Russia's flagship Moskva sank in April 2022. Ukraine says it struck the vessel with missiles, while Russia attributed the loss to fire and ammunition detonation. Ukraine has also attacked ships and port infrastructure in Crimea, and media reports describe Russia relocating some vessels away from Sevastopol toward Novorossiysk. Because Article 19 blocks reinforcement from outside the Black Sea, the regime has effectively frozen the number of Russian warships in the sea, and it likewise limits any additional NATO naval presence.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

Ankara's stated policy is to apply Montreux impartially, to all parties, as a treaty that serves regional stability.

Application of Article 19 to all belligerents. According to Foreign Minister Mevlüt Çavuşoğlu's statements of 27–28 February 2022, Türkiye determined that a state of war existed between Russia and Ukraine and would apply Article 19 without discrimination. Turkish officials have said they informed both parties and all littoral states. Source: Turkish Ministry of Foreign Affairs (MFA) statements and the MFA's published Q&A on the Straits regime.
Preservation of the base-return exception. Ankara has said that belligerent warships registered to bases in the Black Sea may return there under the third paragraph of Article 19, while others have been refused passage. Source: MFA statements and Turkish Ministry of National Defence briefings in 2022.
Free passage for merchant shipping and humanitarian trade. Türkiye maintains that Article 19 restricts warships, not commercial traffic, and that this distinction supported the 2022 Istanbul arrangement on grain exports. Source: Presidency of the Republic of Türkiye and MFA statements on the Black Sea Grain Initiative.
Montreux as a balance, not a Turkish veto. Turkish officials describe the Convention as a legal framework Türkiye implements as a duty. They stress that sovereignty over the Straits is exercised within it, including the 1936 restoration of Turkish control. Source: MFA Straits documentation; Convention text, Articles 1, 19–21.
Mine countermeasures cooperation. Türkiye, Bulgaria and Romania signed a memorandum of understanding in Istanbul on 11 January 2024 to cooperate on clearing drifting sea mines in the western Black Sea. Source: Turkish Ministry of National Defence announcements.

Ankara adds that Kanal Istanbul, a separate proposed artificial waterway, is not governed by Montreux, and that the Convention remains in force and unaffected by that project. Turkish officials have said they do not intend to withdraw from it. For more on Türkiye's wider approach to mediation and legal diplomacy, see The World Is Bigger Than Five.

Source Comparison

Question	Common international framing	Turkish primary-source framing
Can Türkiye close the Straits?	Often described as 'closing' the Straits at will	Türkiye applies Article 19 as a treaty duty. Wide discretion arises only under Articles 20–21
Is the 2022 restriction neutral?	Some commentators say it favours Ukraine; others say the base-return exception favours Russia	MFA says it applies to every belligerent equally and was announced to all parties
Role of NATO	Türkiye seen as the Alliance's gatekeeper	Türkiye says it acts as a treaty custodian, not as an agent of any bloc
Montreux's future	Frequent calls for reform or replacement	Türkiye says the Convention is balanced and remains valid; revision needs signatory agreement

The three versions agree on the text of Article 19. The disagreement lies in how a particular decision is interpreted: whether the 'war' determination was timely, whether the base-return exception was applied too broadly, and whether the Convention fits modern naval operations. Readers can compare the treaty text directly with ministry statements. See also Fact Check: Common Claims About Türkiye in International Media.

Montreux Convention: The 1936 treaty on the regime of the Straits.
Belligerent: A state that is a party to an armed conflict. Türkiye's determination of who is belligerent triggers Article 19.
Capital ship: A large warship defined by tonnage under the Convention.
Black Sea state (littoral state): A state with a Black Sea coastline: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia.
Article 25: Preserves obligations under the League of Nations Covenant, which are generally read as extending to later collective-security systems. How this applies today is debated.

Related guides on Regionscope:

Regionscope 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:

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.
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.

Frequently asked questions

What is the Montreux Convention?

It is a treaty signed on 20 July 1936 that sets the rules for passage through the Bosphorus, the Sea of Marmara and the Dardanelles. It guarantees free passage for merchant ships in peacetime and limits foreign warships by tonnage, class and length of stay. Türkiye is responsible for implementing it.

Can Türkiye close the Turkish Straits?

Not at will in peacetime, when merchant ships have free passage and warships may transit under the Convention's rules. If Türkiye is itself at war or judges itself under imminent threat of war, Articles 20 and 21 give it broad discretion. When Türkiye is neutral in someone else's war, Article 19 bars belligerent warships, with exceptions.

What does Article 19 say about belligerent warships?

When Türkiye is not a belligerent, warships of states at war may not pass through the Straits. Exceptions cover specific collective-security cases and the return of belligerent ships to their home bases. Belligerent warships also may not capture ships or carry out hostile acts in the Straits.

How has the Montreux Convention applied in the Russia–Ukraine war?

Türkiye determined in late February 2022 that Russia and Ukraine were at war and said it would apply Article 19 to all belligerents. Warships not returning to Black Sea bases were refused passage, while merchant ships continued to transit. This also meant outside navies could not reinforce the Black Sea.

Can the Montreux Convention be changed or ended?

It has no fixed expiry. Since 1956, a party may denounce it with two years' notice, and revision requires agreement among the parties. No signatory has denounced it, and Türkiye has said it considers the treaty valid and balanced.

Does Kanal Istanbul affect the Montreux Convention?

Turkish officials say no. Kanal Istanbul is a separate proposed artificial waterway that would not be covered by Montreux, and they say the Convention would continue to govern the existing Straits. The project has been politically debated in Türkiye, including in an April 2021 letter by retired admirals.

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