Diplomatic Briefing· how does Montreux Convention work during war Turkish Straits

The Montreux Convention in Wartime: How Does the Turkish Straits Regime Actually Work?

How does the Montreux Convention work during war? Learn the Turkish Straits rules on warship tonnage, Article 19 and how Türkiye applied them after 2022.

By The Longpeace Editorial Team

Published: October 27, 2026

⏱ 10 min read (2,121 words)

The Brief — Key Takeaways

The 1936 Montreux Convention guarantees free passage for merchant ships through the Turkish Straits in peacetime and keeps that freedom for non-belligerent merchant vessels in wartime.
Montreux limits the tonnage, number and length of stay of warships from non-Black Sea states, and Article 19 bars warships of belligerent states from transit in wartime, subject to narrow exceptions such as return to base.
On 28 February 2022 Türkiye announced that it would apply Article 19 to the Russia–Ukraine war, and Turkish officials say the rule was applied to all states regardless of flag.
Because Montreux keeps the Black Sea's naval balance in the hands of its coastal states, the Convention is widely regarded as a pillar of regional stability, and it has lasted for almost nine decades.
Under Articles 20 and 21, Türkiye holds extra discretion if it is itself a belligerent or believes it faces an imminent danger of war.

Why It Matters

The Montreux Convention works in wartime by keeping the Turkish Straits open to civilian shipping while closing them to the warships of states at war, with narrow exceptions. Since February 2022 it has been the main legal barrier against a wider naval build-up in the Black Sea. Understanding its mechanics explains why Russia, Ukraine, NATO members and others all say they want the regime preserved, even when they disagree on how it is applied.

Background

What the Convention is

The Convention Regarding the Regime of the Straits was signed at Montreux, Switzerland, on 20 July 1936 and entered into force on 9 November 1936. It replaced the Straits arrangements of the 1923 Treaty of Lausanne, which had demilitarized the Straits and placed them under an international commission. Türkiye had asked for a revision as the European security situation deteriorated in the 1930s. The Convention restored full Turkish sovereignty over the Straits, including the right to remilitarize them. The Straits comprise the Dardanelles, the Sea of Marmara and the Bosphorus, which together form the only maritime link between the Black Sea and the Mediterranean.

The original signatories were Bulgaria, France, Greece, Japan, Romania, Türkiye, the United Kingdom (also for its dominions), the Soviet Union and Yugoslavia. Italy acceded in 1938. The Convention has no fixed end date, and it has not been formally amended. Türkiye's own summary of the regime is published by the Ministry of Foreign Affairs.

How the regime works: the core rules

The rules differ by type of vessel and by whether the passing state borders the Black Sea.

Category	Peacetime rule	Wartime rule (Türkiye not a belligerent)
Merchant ships	Free passage by day and night, whatever the flag or cargo (Article 2), with health inspection and fixed tolls	Free passage for ships of non-belligerent states; ships of belligerents may pass if they are not assisting the enemy
Warships of Black Sea states	Passage under notice (eight days) and size limits. Capital ships over 15,000 tons may pass one at a time with up to two destroyers (Article 11). Submarines may pass only to return to base or for repair outside the Black Sea (Article 12)	Same as for non-belligerent states, but belligerent warships are barred (Article 19)
Warships of non-Black Sea states	Fifteen days' notice (Article 13). Each ship is limited to 15,000 tons, with no more than nine ships in transit at once (Article 14). Aggregate force in the Black Sea is capped at about 30,000 tons, rising to a maximum of 45,000 tons, and no single non-Black Sea state may hold more than two-thirds of the cap. Stay is limited to 21 days (Article 18)	Not permitted if the state is a belligerent (Article 19)
Aircraft carriers and capital ships of non-Black Sea states	Not admitted	Not admitted

The tonnage ceilings and 21-day limit were designed to stop outside powers from keeping a permanent fleet in the Black Sea. Submarines of non-Black Sea states cannot enter at all.

The wartime provisions

Three provisions matter most in war:

Article 19: If Türkiye is not at war, warships of belligerent states may not pass through the Straits. Exceptions exist for assistance to a victim of aggression under certain mutual-assistance treaties. Turkish practice also recognizes a return-to-base exception: a warship of a belligerent state may go back to a base registered on the other side of the Straits. Merchant shipping continues.
Article 20: If Türkiye is itself at war, it decides at its own discretion which warships may pass.
Article 21: If Türkiye considers itself threatened with imminent danger of war, it may apply the same discretion.

The Convention also allows the use of the Straits for medical and humanitarian transit and says nothing that prejudices the rights of states under the UN framework. Safety of navigation is regulated separately by Turkish maritime traffic rules, adopted in 1994 and revised in 1998, which govern pilotage, separation schemes and the handling of hazardous cargo in a narrow, densely populated waterway.

Timeline of the Montreux regime in practice

1936: Convention signed (20 July) and enters into force (9 November).
1939–1945: Türkiye, neutral for most of the Second World War, kept belligerent warships out of the Straits.
1945–1946: Soviet demands for a revised regime and a joint defence role were rejected by Türkiye, which was supported by the Western powers.
1991 onward: The Soviet collapse leaves Russia, Ukraine and Georgia as new Black Sea coastal states, while Romania and Bulgaria later join NATO.
2008: During the Russia–Georgia war, Türkiye applied the tonnage rules to US hospital ships, which was a notable test of the limits.
28 February 2022: Türkiye announces that Article 19 will be applied to the Russia–Ukraine war.

For wider context on how Türkiye's treaty record fits together, see Treaties That Keep the Peace: Why Montreux, Lausanne and Kars Have Lasted. An independent primer is also available from Region Scope.

Key Players & Positions

How Türkiye applied it after February 2022

Ukraine asked Türkiye in late February 2022 to close the Straits to Russian warships. On 28 February, Foreign Minister Mevlüt Çavuşoğlu said that the situation in Ukraine met the criteria for a war under Article 19, and that Türkiye would apply the provision. Ankara informed the coastal and non-coastal states and asked them not to send warships through the Straits. Turkish officials said the closure applied to every belligerent, and the return-to-base exception was kept.

The decision therefore did not depend on who the belligerent was. Turkish officials said that requests from several states, including Russia, were declined when the ships were not returning to home bases in the Black Sea. Russia, as a Black Sea power with its fleet headquartered in Sevastopol, was in practice more affected on one side, while NATO members were affected on the other because their ships were outside the cap.

Ukraine

Kyiv has repeatedly urged Türkiye to apply the Convention strictly and has welcomed the closure to Russian warships. Ukraine has also pushed for Montreux to be read as covering the movement of reinforcement vessels. At the same time, naval assistance to Ukraine from third countries, such as the transfer of minehunters by NATO members, has not been delivered through the Straits since the war began, which Ankara cites as evidence that it is applying the rules evenly.

Russia

Moscow's official line is that it respects the Convention and wants it preserved. Russian officials have warned against third-country moves they see as changing the Black Sea balance, and have criticized the growing NATO presence in the region. Russia has also at times argued that Western states were using the war to reinterpret Montreux, though Moscow's own dependence on the Black Sea Fleet makes the return-to-base rule significant to it.

NATO and its members

NATO states with Black Sea coasts, namely Türkiye, Romania and Bulgaria, have kept naval deployments in line with the Convention. Allies outside the Black Sea have accepted the limits and have used air and surveillance assets instead. In January 2024 Türkiye, Romania and Bulgaria signed an agreement in Ankara to set up a Black Sea Mine Countermeasures Force, a regional arrangement that works within the Montreux framework rather than around it. Some NATO capitals have said that they want a stronger presence on the Black Sea, but they have not formally asked for a revision of the Convention.

Other states

Georgia, which is a Black Sea coastal state, and other states with maritime interests have generally welcomed the stability the Convention provides. A few commentators in Western media and academia have suggested that Montreux should be revised to reflect modern shipping and naval technology, but no signatory has formally proposed it.

🇹🇷 Diplomatic Role · Mediation & Treaty Record

Türkiye's Role

Ankara presents itself as the guardian of the Straits regime, not as a party to the conflict. The following points summarize official Turkish policy as stated by Turkish primary sources.

Impartial implementation. According to the Turkish Foreign Ministry, Türkiye applies Montreux to all states and all warships equally, and the decision of 28 February 2022 was made under Article 19 and was not directed against any state. The Ministry's statements and the Foreign Minister's press remarks are the primary source for this position.
Sovereignty restored by treaty. Ankara points out that Montreux ended the demilitarized Straits arrangement of Lausanne and restored Turkish sovereignty over the Straits in 1936, and that the Convention is a balanced instrument which reflects the interests of the Black Sea states as well as those of maritime powers.
Preserving the Black Sea balance. The Presidency and the Ministry of National Defence have said that the regime prevents a naval arms race in a semi-enclosed sea, and that opening the Straits to the warships of belligerents would risk the war spreading into the Black Sea and the Mediterranean.
Diplomacy alongside the regime. Türkiye links the application of Montreux to its mediation. It hosted the 2022 Istanbul negotiations and was a co-architect of the Black Sea Grain Initiative, under which more than 33 million tons of grain reached world markets. See What Happened at the 2022 Istanbul Talks Between Russia and Ukraine? and Mediation Files: How Türkiye Brokers Talks Between Adversaries.
Legal basis. The positions above rest on the text of the 1936 Convention (notably Articles 2, 19, 20 and 21) and on Türkiye's sovereign right to regulate navigation in the Straits for safety and environmental protection.

For the question of whether Türkiye can credibly be a neutral mediator while also controlling the Straits, see the Fact Check on Türkiye's mediation role. It is a separate page that is not repeated here.

Source Comparison

Coverage of the Straits since 2022 has been broadly consistent on the facts but differs in emphasis.

Question	Common international framing	Turkish primary sources
Why was the Straits closed?	Often described as 'Türkiye closing the Straits to Russia'	Described as the application of Article 19 to all belligerents, announced in a general notification
Who is affected?	Mostly presented as hurting Russia's naval reinforcement	Stressed as neutral: every belligerent and every flag is covered, with the return-to-base exception
Is Montreux outdated?	Some analysts say it should be updated for modern naval technology and the Black Sea's new states	Ankara sees the text as sound and says its strength lies in its stability
What about NATO ships?	Debated as a limit on allied presence	Seen as one reason the Black Sea has not become a theatre of wider naval confrontation
Role of Türkiye	Mixed: praised as a gatekeeper, questioned for ties with Moscow	Presented as a treaty-based, impartial implementer and mediator

Independent analyses from sister publications go into more detail, including Bloc Politics on Montreux and Black Sea access and The Political Anatomy on Article 19.

Readers should check texts against the Convention itself, which is published in treaty collections and on the Turkish Foreign Ministry's website, and should distinguish statements of fact from statements of position. The approach is described in Editorial Principles: Sources, Fact–Position Separation and Corrections.

Turkish Straits: the Bosphorus, the Sea of Marmara and the Dardanelles, which connect the Black Sea to the Mediterranean.
Non-Black Sea state: a country with no Black Sea coast. Its warships face tonnage, duration and notice limits.
Belligerent: a state engaged in war, whether or not a formal declaration has been made. Ships of belligerents face the Article 19 restriction.
Return-to-base exception: the allowance for a belligerent's warship to go back to its registered base on the other side of the Straits.
Article 19 / 20 / 21: the wartime rules, applying respectively when Türkiye is not at war, is at war, or faces imminent danger of war.

Frequently asked questions

Does the Montreux Convention close the Turkish Straits in wartime?

Not entirely. It keeps the Straits open to merchant ships of non-belligerent states, but under Article 19 it bars warships of belligerent states when Türkiye is not at war. If Türkiye is itself at war, or fears imminent danger of war, Articles 20 and 21 give it wider discretion.

What is the return-to-base exception?

It allows a belligerent's warship to return to a base registered on the other side of the Straits. In 2022 Turkish officials said that the exception remained in place, but that ships which were not returning to their home bases could not pass.

What limits does Montreux place on warships of non-Black Sea states?

Each ship may not exceed 15,000 tons, no more than nine may transit at once, and 15 days' notice is required. Their combined force in the Black Sea is capped at about 30,000 tons, rising to a maximum of 45,000 tons, and no ship may stay longer than 21 days. Aircraft carriers and submarines of non-Black Sea states are not admitted.

Did Türkiye close the Straits only to Russia?

According to Turkish officials, no. Ankara announced on 28 February 2022 that it would apply Article 19 to all belligerents and notified coastal and non-coastal states in general terms. Practical effects were heaviest for Russia and for any state that wished to send warships into the Black Sea.

Why is Montreux seen as a pillar of Black Sea stability?

It keeps outside naval power in the Black Sea limited and gives Black Sea states a larger say in the sea's naval balance. This has helped prevent an arms race there through the Cold War and the post-2022 period, and none of the major powers has formally asked for a revision.

Can Montreux be changed?

The Convention contains revision and denunciation procedures, but they require the agreement of the parties and none has formally proposed a change. Some analysts have called for an update, while Türkiye and many others say its current terms work well.

Cross-Publication Perspectives & Cited Research

Related Dossiers Across Partner Publications

4 Partner Desks