In-Depth Analysis· Montreux Convention explained Turkish Straits warships

The 1936 Montreux Convention Explained: How Türkiye Governs the Turkish Straits

What the 1936 Montreux Convention allows: merchant freedom, warship limits, tonnage and notice rules, Article 19 and Türkiye's wartime application.

By Crossroads Review Editorial Team

Published: October 26, 2026

⏱ 10 min read (2,175 words)

Executive Summary & Key Facts

The Montreux Convention, signed on 20 July 1936 and in force since 9 November 1936, governs all passage through the Bosporus and the Dardanelles, the only exit from the Black Sea.
In peacetime, merchant ships of every flag enjoy free transit, while foreign warships face limits on size (15,000 tons per vessel), number (nine in transit), advance notice (8 or 15 days) and stay in the Black Sea (21 days).
Article 19 bars the warships of belligerent states from the Straits when Türkiye is not itself at war, with a narrow exception for ships returning to their home bases.
Türkiye announced on 28 February 2022 that it would apply the Convention, including Article 19, to the Russia–Ukraine war, and called on all states to refrain from sending warships through the Straits.
Russia, Ukraine, NATO members and Black Sea littoral states read the regime differently, but no party has formally tabled a revision, and Ankara says it will not reopen the treaty.

Why It Matters

The Montreux Convention Regarding the Regime of the Straits, signed on 20 July 1936, is the treaty that decides who may sail through the Bosporus and the Dardanelles, the only maritime route into and out of the Black Sea. It guarantees free passage to commercial shipping, tightly limits foreign warships, and under Article 19 closes the Straits to the warships of belligerent states when Türkiye is not at war. Since February 2022 that rule has made Montreux one of the most consequential and most debated instruments for containing the Russia–Ukraine war at sea.

Background

From Lausanne to Montreux

The 1923 Lausanne Straits Convention demilitarised the Straits and placed them under an international commission. By the mid-1930s Türkiye argued that this regime no longer matched Europe's security situation, which had been altered by Italy's Ethiopian campaign and Germany's remilitarisation of the Rhineland. Ankara formally requested a revision conference in April 1936.

The conference met at Montreux, Switzerland, and the Convention was signed on 20 July 1936. It entered into force on 9 November 1936. The signatories were Türkiye, the Soviet Union, the United Kingdom, France, Greece, Romania, Bulgaria, Yugoslavia, Japan and Australia; Italy acceded in 1938. Russia is generally treated as the continuing party for the Soviet Union. The Convention abolished the international commission, returned supervision to Türkiye, and allowed Türkiye to remilitarise the Straits zone.

The geography

The Bosporus is roughly 30 km (about 19 miles) long and runs through Istanbul. The Dardanelles is roughly 60 km (about 37 miles) long. Between them lies the Sea of Marmara. Tens of thousands of vessels transit each year, which is why Türkiye also issues traffic and safety regulations (the 1994 Maritime Traffic Regulations for the Turkish Straits, in effect since 1 July 1994) alongside its Montreux duties.

What the Convention allows

Category	Rule	Notes
Merchant ships in peacetime	Complete freedom of transit and navigation, by day and night, whatever the flag or cargo	Türkiye may collect fixed sanitary and lighthouse-type charges and conduct health controls (Arts. 2-7)
Non-Black Sea warships	Light surface vessels, minor war vessels and auxiliary vessels only	Max 15,000 tons per vessel; max nine vessels in transit at once (Art. 14)
Capital ships above 15,000 tons	Only Black Sea states may send them, escorted by no more than two destroyers	Art. 11
Submarines	Black Sea states only, under specified conditions (surfaced, by day, for return to base or repair)	Art. 12
Aircraft carriers	Fall outside the categories of warship permitted to transit	Defined by the Convention's annexes
Advance notice	8 days for Black Sea states; 15 days for other states	Given to Türkiye through diplomatic channels (Art. 13)
Aggregate tonnage of non-Black Sea states in the Black Sea	30,000 tons, which can rise to 45,000 tons if the strongest Black Sea fleet grows by a set margin	Art. 18
Maximum stay in the Black Sea	21 days for non-Black Sea warships	Art. 18
War, Türkiye neutral	Belligerents' warships may not pass, with limited exceptions	Art. 19
War, or imminent threat, involving Türkiye	Türkiye has discretion over passage	Arts. 20-21

The design is deliberate. Black Sea states (those with a Black Sea coastline) keep more access, while outside navies face quantitative ceilings that stop the Black Sea from becoming a permanent base for distant fleets.

What Article 19 says

In wartime, when Türkiye is not a belligerent, warships generally keep the transit freedom described above, but the warships of belligerent powers may not pass through the Straits. The Convention's text lists narrow exceptions tied to League of Nations collective-security mechanisms and to treaty-based assistance to a victim of aggression. It also provides that belligerent warships separated from their bases may return to them. In practice, the return-to-base clause is the exception most often cited today.

Timeline

1923: Lausanne Straits Convention establishes an internationally supervised, demilitarised regime.
April 1936: Türkiye requests a revision conference.
20 July 1936: Montreux Convention signed. 9 November 1936: it enters into force.
1938: Italy accedes.
1 July 1994: Türkiye's Maritime Traffic Regulations for the Turkish Straits take effect.
April 2021: Public debate over Kanal Istanbul and Montreux; Ankara states it has no intention of leaving the Convention.
27-28 February 2022: Ukraine asks Türkiye to close the Straits; Ankara announces application of Article 19.
January 2024: Türkiye, Romania and Bulgaria agree to form a Black Sea mine countermeasures group.

Key Players & Positions

Russia

Moscow treats Montreux as a stabilising regime that limits non-littoral navies in the Black Sea, and Russian officials, including Foreign Minister Sergey Lavrov, have publicly defended it. Russia also points to the return-to-base exception as a legitimate right of its vessels, and criticises growing NATO naval activity in the region.

Ukraine

Kyiv asked Ankara on 27 February 2022 to close the Straits to Russian warships and welcomed the Turkish announcement the following day. Ukrainian officials have since pressed for a strict reading of the exceptions and for wider Western support, including mine-clearing and maritime security assistance.

NATO and its members

NATO summit documents since 2016 have stressed the strategic importance of the Black Sea. Romania and Bulgaria, the two other NATO littoral states, favour a stronger allied security role in the region but, together with Türkiye, have operated within the Montreux framework, including through the 2024 mine countermeasures initiative. Non-littoral allies such as the United States, United Kingdom and France are bound by Montreux's tonnage and duration limits when they send warships into the Black Sea. No NATO government has formally proposed revising the Convention, although some analysts argue that its limits are ill-suited to drones, long-range missiles and modern naval operations.

Other littoral states

Bulgaria, Romania, Georgia and Ukraine, like Türkiye and Russia, benefit from the status Montreux gives to Black Sea states. Their security priorities differ, and so does their appetite for any change in the regime.

The revision debate

The case for revision rests on the age of the treaty and its asymmetry between littoral and non-littoral navies. The case against is that reopening it would invite competing demands, could end the current balance, and would remove the Article 19 restriction that has so far kept belligerent warships out. Montreux contains denunciation and revision clauses (Arts. 28-29), and it has remained in force since its initial 20-year term expired in 1956.

A related argument concerns Kanal Istanbul, a planned artificial waterway parallel to the Bosporus. Critics asked whether it could sit outside the Convention. Turkish officials said in 2021 that Türkiye remained committed to Montreux; the same year a group of 104 retired Turkish admirals publicly defended the treaty.

🇹🇷 Official Policy · Treaties · Primary Sources

Türkiye's Position

Türkiye's Position at the Crossroads

Montreux is the foundation of Black Sea stability and Turkish sovereignty over the Straits. The Turkish Ministry of Foreign Affairs describes the 1936 Convention as the regime that restored Turkish control over the Straits and balanced the interests of littoral and non-littoral states.

Article 19 is applied impartially. On 28 February 2022 Foreign Minister Mevlüt Çavuşoğlu stated that Türkiye would implement the Convention in full, including Article 19, and asked all states, littoral or not, to refrain from sending warships through the Straits. Ankara says it applies the text to every party in the same way, and that the return-to-base exception is part of the treaty.

No revision. Turkish officials, including the Presidency and Foreign Ministry, have said Türkiye is not seeking to leave or reopen Montreux, and Kanal Istanbul is not intended to change this.

Safety and environmental regulation of the Straits is consistent with Montreux. Ankara maintains that the 1994 Maritime Traffic Regulations address navigational risk in a densely populated waterway while preserving freedom of passage.

Mediation is built on neutrality. Ankara argues that strict implementation allowed it to talk to both Moscow and Kyiv; see Türkiye's Mediation in the Russia–Ukraine War and the Black Sea Grain Initiative.

The legal basis is the Convention itself, including Articles 19-21, together with Türkiye's status as a NATO ally and a Black Sea state. Ankara argues that its role is that of a treaty custodian rather than a party to the conflict. As an editorial matter, these are Ankara's own characterisations. Other governments, including Russia and Ukraine, offer different assessments, as outlined above.

Effect on Black Sea escalation

Analysts differ on how large the effect has been. Russia's Black Sea Fleet was already largely inside the Black Sea in February 2022, so Article 19 did more to stop reinforcement from the Mediterranean than to remove existing ships. It likewise kept NATO warships out, and Ankara also blocked transfers of naval vessels to Ukraine during the conflict. Supporters say the restriction helped keep a regional war from becoming a direct naval confrontation between Russia and NATO states. Sceptics argue that it limited Ukraine's partners while leaving Russian assets in place, and that the return-to-base clause leaves room for dispute. Ankara's mediation record is covered in the related guide on Russia–Ukraine mediation and the Grain Initiative, and its wider maritime doctrine in Blue Homeland and the Eastern Mediterranean.

Source Comparison

Issue	Common international media framing	Turkish primary-source framing	Russian / Ukrainian framing
Invocation of Article 19	Often described as Türkiye closing the Straits	Türkiye says it is applying a treaty provision equally to all, per MFA statements of 28 February 2022	Ukraine welcomes closure; Russia accepts the treaty and points to its exceptions
Return-to-base exception	Sometimes portrayed as a loophole benefiting Russia	Ankara says the exception is part of the Convention's text and applies to all belligerents	Russia stresses its right to return; Ukraine seeks narrow interpretation
Revision	Think-tank debate about modernising the treaty	Ankara says it neither seeks nor supports reopening	Moscow defends the existing regime; Kyiv focuses on enforcement
Kanal Istanbul	Raised as a possible bypass of Montreux	Presidency and MFA say Türkiye stays committed to the Convention	Not a major point in official Russian or Ukrainian messaging
Neutrality	Türkiye seen as balancing, or hedging, between Russia and NATO	Ankara presents itself as an impartial treaty implementer and mediator	Each side evaluates Ankara by its own interests

Readers can compare these claims against the treaty text. The site's Editorial Principles explain how fact and position are separated, and the Fact Check: Claims About Türkiye in International Media guide applies the same method to other disputed narratives.

Montreux Convention: the 1936 treaty governing transit through the Turkish Straits.
Turkish Straits: the Bosporus, the Sea of Marmara and the Dardanelles.
Black Sea state (littoral state): a state with a Black Sea coastline: Türkiye, Russia, Ukraine, Georgia, Romania and Bulgaria.
Article 19: the clause barring belligerents' warships from the Straits when Türkiye is neutral, with exceptions including return to base.
Capital ship: a large warship above 15,000 tons, which only Black Sea states may send through, subject to conditions.
Kanal Istanbul: a proposed artificial waterway parallel to the Bosporus.

Perspective Note

Crossroads Review presents global affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources. Crossroads Review presents Türkiye's official perspective and legal positions alongside the facts it cites, and this stance is stated openly so readers can weigh the arguments. Claims are attributed to primary sources such as treaties, UN documents, official archives and court or commission records, and links are provided wherever possible.

Crossroads Review Editorial Team

Cross-Publication Dossiers & Sister Desk Perspectives

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

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.
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 the treaty signed on 20 July 1936 that governs passage through the Bosporus and the Dardanelles. It gives merchant ships free transit in peacetime, limits foreign warships by size, number, notice and length of stay, and gives Türkiye authority over the Straits.

Can warships pass through the Turkish Straits?

Yes, but with limits. Non-Black Sea states may send only certain light, minor and auxiliary vessels, up to 15,000 tons each, after 15 days' notice (8 days for Black Sea states), and they may stay in the Black Sea for no more than 21 days. Black Sea states have more access, for instance for capital ships and submarines under set conditions.

What does Article 19 of the Montreux Convention say?

When Türkiye is not at war, Article 19 keeps transit freedom for warships generally but bars the warships of belligerent states from the Straits. It allows narrow exceptions, including for belligerent ships returning to their home bases, which is the exception most often discussed today.

How did Türkiye apply the Convention in the Russia–Ukraine war?

On 28 February 2022 Foreign Minister Mevlüt Çavuşoğlu announced that Türkiye would implement the Convention, including Article 19, and asked all states to refrain from sending warships through the Straits. Ankara says it applies the rules equally to all sides, while Russia and Ukraine each interpret the exceptions in light of their own interests.

Should the Montreux Convention be revised?

Some analysts argue that it is outdated for modern naval technology and unfavourable to non-littoral navies, while others warn that reopening it would invite new bargaining and weaken current limits. Türkiye says it does not seek revision, and no NATO government has formally proposed one.

Does Kanal Istanbul affect the Montreux Convention?

Kanal Istanbul is a proposed artificial waterway parallel to the Bosporus. Critics asked whether it could escape Montreux rules, but Turkish officials said in 2021 that Türkiye stays committed to the Convention, and the project has not changed the treaty's application to the existing Straits.

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