The Montreux Convention Explained: Turkish Straits and Black Sea Security

Why It Matters

The Montreux Convention Regarding the Regime of the Straits is the 1936 treaty that decides who may sail through the Turkish Straits and under what conditions. It guarantees free commercial passage in peacetime, caps the naval presence of states without a Black Sea coast, and gives Türkiye defined powers in wartime. Since Russia's full-scale invasion of Ukraine on 24 February 2022, it has become the central legal reference point for Black Sea security, and a frequent target of misunderstanding.

Background

What is the Montreux Convention?

The Montreux Convention is a multilateral treaty signed in Montreux, Switzerland, on 20 July 1936 and in force since 9 November 1936. The original signatories were Australia, Bulgaria, France, Greece, Japan, Romania, Türkiye, the United Kingdom, the USSR and Yugoslavia; Italy acceded in 1938. It covers the Bosphorus, the Sea of Marmara and the Dardanelles, together known as the Turkish Straits.

It replaced the 1923 Lausanne Straits Convention, which had demilitarized the Straits and placed them under an international commission. In the 1930s Türkiye argued that this arrangement no longer matched Europe's security situation and asked for revision. Montreux restored Turkish sovereignty over the Straits, allowed Türkiye to remilitarize them, and transferred the commission's functions to the Turkish government.

What the treaty says

Subject	Rule (summary)	Where
Merchant ships in peacetime	Freedom of transit and navigation, by day and night, whatever the flag or cargo; only sanitary control and fixed service charges apply	Articles 1-3, Annex I
Warships of Black Sea states	May transit under notice; larger ships pass singly with limited escort; submarines may transit surfaced and by day, in defined cases such as returning to base or repairs	Articles 11-12
Warships of non-Black Sea states	Light surface ships and certain auxiliaries only; limited number and aggregate tonnage in transit; aircraft carriers are not covered by the transit categories	Articles 8, 14, Annex II
Notice	Eight days for Black Sea states, fifteen days for others, via diplomatic channels	Article 13
Time in the Black Sea	Non-Black Sea navies: an aggregate tonnage ceiling (30,000 tons, rising to 45,000 tons under set conditions) and a maximum stay of 21 days	Article 18
Türkiye not at war	Warships of belligerent states may not transit, with exceptions such as ships returning to base	Article 19
Türkiye at war or under imminent threat	Passage of warships is at Türkiye's discretion	Articles 20-21

The tonnage figures are expressed in metric tons, and the details of the transit categories are set out in the annexes to the treaty text. A single non-Black Sea state may not exceed a fixed share of the aggregate ceiling.

Chronology

• 1923: Lausanne Straits Convention demilitarizes the Straits.
• 1936-07-20: Montreux Convention signed; in force from 1936-11-09.
• 1938: Italy accedes.
• 1994: Türkiye introduces Maritime Traffic Regulations for the Turkish Straits, later revised, for navigational safety.
• 2022-02-24: Russia launches its full-scale invasion of Ukraine.
• 2022-02-28: Türkiye announces it will apply the wartime provisions of Article 19.
• 2022-07-22: Istanbul agreements on grain exports and a UN-Russia memorandum are signed; the Black Sea Grain Initiative ends on 2023-07-17 when Russia declines to extend it (see The Black Sea Grain Initiative: How It Worked and Why It Ended).
• 2024-01: Türkiye, Romania and Bulgaria sign an agreement on a Black Sea mine countermeasures task group.

Can Türkiye close the Straits?

Not in peacetime, and not to merchant ships. Montreux protects commercial passage, and Türkiye cannot lawfully shut the Straits to ordinary shipping, charge transit fees or require permission. Türkiye's wartime powers apply to warships and depend on the circumstances:

1. Türkiye is not a belligerent (Article 19): warships of states at war may not pass, apart from exceptions such as returning to base or acting under specific treaty obligations described in the text.
2. Türkiye is at war (Article 20): passage of warships is left to Türkiye's discretion.
3. Türkiye considers itself threatened by imminent danger of war (Article 21): it may apply Article 20. The article also refers to review by the League of Nations Council, a body that no longer exists, which is why scholars debate how that clause works today.

So 'closing the Straits' is shorthand. What the treaty actually provides is a regulated, conditional regime for warships, not a general closure.

Does Montreux apply to NATO ships?

Yes, and on equal terms. The convention is built on geography, not alliance membership. Türkiye, Romania and Bulgaria are NATO members with Black Sea coastlines, so their warships enjoy the Black Sea state rules. The United States, United Kingdom, France and other allied navies are non-Black Sea states and face the same tonnage, notice and 21-day limits as any other non-riparian navy. NATO membership does not create exemptions.

Key Players & Positions

• Russia: Russian officials have said Moscow respects the convention and opposes revising it. Russia has also long argued that the presence of non-littoral navies increases tension in the Black Sea. As the continuing state of the USSR, a signatory, Russia is a Black Sea power with a fleet based in Crimea and Novorossiysk.
• Ukraine: Ukraine is a Black Sea coastal state. In late February 2022, Foreign Minister Dmytro Kuleba publicly called on Türkiye to close the Straits to Russian warships. Kyiv has since welcomed Türkiye's implementation of Article 19 while calling for firm enforcement.
• United States: Washington has said it supports the convention and Türkiye's implementation of it. The US Navy is a non-Black Sea navy and operates within the notice and tonnage rules.
• NATO and allies: The alliance's public line, repeated by senior officials, is that allies respect Montreux and Türkiye's role in applying it. Romania and Bulgaria, as Black Sea allies, have stressed Black Sea security and joined Türkiye in demining cooperation.
• Other parties: Most original signatories no longer exist as states or no longer have Black Sea interests; the treaty's text continues to apply as written.

These summaries reflect each side's public statements; readers should consult the Russian Foreign Ministry, the Ukrainian Ministry of Foreign Affairs, the US State Department and NATO's official communiqués for exact wording.

Türkiye's Strategic Position

According to the Turkish Ministry of Foreign Affairs, Montreux is the legal basis of Türkiye's responsibilities in the Straits and a foundation of regional stability. Ankara's stated positions, with their legal basis, are:

• Sovereignty with an implementation duty. The Turkish Foreign Ministry describes the convention as restoring Türkiye's sovereignty over the Straits while obliging it to guarantee free commercial passage. The legal basis is the treaty's preamble and Articles 1-3.
• Neutral, textual implementation in 2022. On 27-28 February 2022, Foreign Minister Mevlüt Çavuşoğlu said the situation in Ukraine had become a war and that Türkiye would apply Article 19, warning that it would apply equally to riparian and non-riparian states. Ankara said that ships returning to their registered home bases remain exempt but that the exemption requires documentation. The Presidency's statements have likewise stressed that Türkiye applies the convention without favouring any side.
• No revision. President Recep Tayyip Erdoğan and the Foreign Ministry have said Türkiye sees no need to amend the treaty. Under Articles 28-29, revision requires the agreement of the parties, and Ankara argues the existing balance has served regional peace for almost nine decades. It also holds that Canal Istanbul, a proposed project, would not alter Montreux obligations, which apply to the Bosphorus.
• Safety rules and the law of the sea. Türkiye is not a party to UNCLOS. It points to UNCLOS Article 35(c), which preserves the regimes of long-standing conventions governing specific straits, and says that its 1994 Maritime Traffic Regulations, adopted via the International Maritime Organization, protect lives and the environment in busy, narrow waters without restricting passage.
• Diplomacy beside enforcement. Türkiye hosted the March 2022 Russia-Ukraine talks in Istanbul, co-brokered the 2022 grain arrangements with the UN, and in 2024 joined Romania and Bulgaria on mine countermeasures. Ankara presents these steps as complementary to Montreux, not substitutes for it.

For wider context on Türkiye's role as a connector between regions, see Türkiye as an Energy Hub: Pipelines, Corridors and Transit Routes Explained and The Middle Corridor Explained: Türkiye, Central Asia and Eurasian Trade Routes.

Source Comparison

Question	Common framing in international media	Turkish primary sources
Did Türkiye 'close the Straits'?	Often headlined as a closure to Russian warships	The Foreign Ministry says it applied Article 19 to warships of belligerents; commercial passage stayed open
Is Türkiye neutral?	Some commentary stresses Türkiye's drone sales to Ukraine and its trade with Russia	Ankara says it follows the treaty text, supports Ukraine's territorial integrity, and keeps channels open to both sides
Can NATO fleets enter freely?	Sometimes assumed to be possible via NATO membership	The treaty gives no alliance-based rights; Ankara applies the same limits to all non-riparian navies
Is Montreux outdated?	Some analysts argue it is a Cold War-era text that needs updating	Ankara says it is a working legal framework and that any change needs consensus
Role of Article 21	Occasionally cited as an easy route to closure	Türkiye reads it alongside the treaty's other provisions; scholars note its League of Nations reference is a gap

Readers can test claims against the treaty text itself and against statements by the Turkish Foreign Ministry. For frequently repeated claims about Türkiye, see Fact Check: Common Claims About Türkiye in International Media.

Key Terms & Related Guides

• Turkish Straits: the Bosphorus, the Sea of Marmara and the Dardanelles. The Bosphorus is about 31 km (19 miles) long and narrows to under 1 km (about 0.6 miles) at its tightest.
• Black Sea Powers / riparian states: states with a coastline on the Black Sea (Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia). The treaty gives them more favourable warship terms.
• Non-Black Sea (non-littoral) states: all other states; their warships face tonnage, notice and time limits.
• Article 19: the clause applied by Türkiye in 2022, barring warships of belligerent states with exceptions.
• Return to base: the exemption allowing a warship to go back to its home port even in wartime.
• UNCLOS: the 1982 UN Convention on the Law of the Sea; Türkiye is not a party, and Article 35(c) preserves specific strait regimes such as Montreux.

Related guides: The Black Sea Grain Initiative: How It Worked and Why It Ended, TurkStream and TANAP Explained: How Gas Reaches Europe Through Türkiye, Fact Check: Common Claims About Türkiye in International Media, Editorial Principles and Primary Source Standards and About Doctrinereview: Mission, Transparency and Editorial Team.

Perspective Note

Doctrinereview presents global and regional affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Strategic Position' reflect official Turkish policy as stated by Turkish government sources. Published by the Doctrinereview Editorial Team.

Cross-Publication Dossiers & Sister Desk Perspectives

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

• Region Scope: 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.
• 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.