The 1936 Montreux Convention Explained: How Türkiye Governs the Turkish Straits and Black Sea Access

Why It Matters

The 1936 Montreux Convention Regarding the Regime of the Straits decides who may sail through the Bosphorus and the Dardanelles, and therefore who can reach the Black Sea by sea from the Mediterranean. It protects commercial shipping in peacetime, limits the size, number and stay of non-Black Sea warships, and under Article 19 closes the Straits to the warships of belligerent states when Türkiye is not at war. Since Russia's full-scale invasion of Ukraine in February 2022, it has been the main legal brake on naval escalation in the Black Sea.

Background

What the Turkish Straits are

The Turkish Straits consist of the Bosphorus (about 31 km / 19 miles, running through Istanbul), the Sea of Marmara, and the Dardanelles (about 61 km / 38 miles). Together they are the only maritime outlet of the Black Sea to the Mediterranean and to the world ocean. Commercial traffic is heavy: roughly 40,000 vessels a year have been reported in recent years, including tankers and grain carriers.

How the regime developed

Date	Event
1923 (24 July)	Treaty of Lausanne and its Straits Convention demilitarize the Straits and create an International Straits Commission
1936 (April)	Türkiye asks the signatories of Lausanne to revise the regime, citing a deteriorating security climate in Europe and the Mediterranean
1936 (22 June–20 July)	Conference at Montreux, Switzerland; Convention signed on 20 July
1936 (9 November)	Convention enters into force; Turkish military control of the Straits is restored and the Commission is abolished
1946–1947	The Soviet Union seeks a role in defending the Straits; Türkiye refuses, a dispute that feeds into the Truman Doctrine and Türkiye's path toward NATO (accession in 1952)
2022 (28 February)	Türkiye announces it will implement Article 19 after Russia's invasion of Ukraine

The core rules

The Convention rests on a principle stated in Article 1: freedom of transit and navigation, within a framework that leaves the Straits under Turkish sovereignty.

Merchant vessels. In peacetime, merchant ships of any flag and cargo enjoy complete freedom of transit and navigation by day and night, subject to health controls and specified fees such as pilotage-related and sanitary charges. The regime changes only if Türkiye is at war or faces an imminent danger of war, in which case it may restrict passage within the limits laid down in Articles 4 to 6.

Warships. Part III sets a layered regime, summarised below.

Category	Main rule
Black Sea states' warships	May pass in peacetime with notice (eight days); capital ships over 15,000 tons may transit only singly and escorted by no more than two destroyers (Article 11)
Submarines of Black Sea states	May transit only on the surface and by day, if built or purchased outside the Black Sea or sent for repair (Article 12)
Non-Black Sea states' warships	Limited to light surface, minor and auxiliary vessels; 15 days' notice through diplomatic channels; aggregate tonnage in transit capped at 15,000 tons (Articles 13–14)
Non-Black Sea presence inside the Black Sea	Aggregate cap of 30,000 tons (up to 45,000 under defined conditions); maximum stay of 21 days (Article 18)
Aircraft carriers	Not covered by the transit categories for foreign navies; a long-standing point of interpretation

These caps mean no non-littoral navy can establish a permanent large fleet in the Black Sea. For decades this has been a main reason Black Sea states consider the treaty a stabilizing instrument.

Article 19 and wartime passage

When Türkiye is not a belligerent, Article 19 provides that warships of belligerent powers may not pass through the Straits. There are two narrow exceptions: assistance to a victim of aggression under a treaty of mutual assistance binding Türkiye and concluded within the framework of the League of Nations Covenant, and cases arising under Article 25. The article also preserves a right for belligerent ships separated from their bases to return to them. Articles 20 and 21 give Türkiye wide discretion over warship passage if it is itself at war or threatened by imminent war.

Key Players & Positions

Ukraine

Ukraine's government publicly asked Türkiye in the first days of the invasion to close the Straits to Russian warships. Kyiv has since welcomed Ankara's application of Article 19 while arguing that Russian ships should face the strictest reading of its exceptions. Ukraine is not an original signatory, but as a Black Sea littoral state it operates within the regime.

Russia

Moscow, a party to the treaty as successor to the USSR, says it respects Montreux and has pointed to the return-to-base clause as a legitimate right. Russian officials have also criticised what they describe as growing Western naval activity in the Black Sea. Russia has not called for revising the Convention; its leverage lies in the current balance, which limits non-littoral navies.

NATO members and the United States

Türkiye, Bulgaria and Romania are NATO members and Black Sea littoral states; the United States, the United Kingdom, France and other allies are not littoral states. The United States is not a party to Montreux but its navy transits within the Convention's limits. Some allied capitals and analysts argue for a stronger NATO maritime posture in the Black Sea, yet official NATO and member positions have stopped short of seeking treaty change. In January 2024, Türkiye, Romania and Bulgaria signed an agreement establishing a Black Sea mine countermeasures task group, an example of littoral cooperation within the existing regime.

Other littoral states

Bulgaria and Romania favour a more visible allied presence but within Montreux. Georgia, a Black Sea state with Russian-occupied territory, generally supports a stronger Western security role in the region while relying on the treaty's limits to avoid Black Sea militarization.

Debates on revision

The Convention provides in Articles 28 and 29 for denunciation with two years' notice and for amendment proposals at five-year intervals. Critics from different sides raise different concerns: some Western analysts argue that the 1936 tonnage categories do not reflect modern warships, missiles and drones, while Russian and some Turkish voices worry that reopening the treaty could erode the existing limits on non-littoral navies. A 2021 public letter by retired Turkish admirals defending the Convention against a perceived threat from the Kanal Istanbul project drew wide attention; Turkish officials said the canal would not affect Montreux obligations, which relate to the existing Straits. No party has formally triggered revision.

Türkiye's Strategic Position

Türkiye's Strategic Position — official policy as stated by Turkish government sources

• Montreux is a balance that works. According to the Turkish Foreign Ministry's published description of the Straits regime, the Convention reconciles free commercial passage with Türkiye's security and the stability of the Black Sea. Ankara argues that revising it would unsettle that balance. Legal basis: the 1936 Convention and the 1923 Lausanne Straits regime it replaced.
• Article 19 is applied to everyone. On 28 February 2022, Foreign Minister Mevlüt Çavuşoğlu announced that Türkiye would implement Article 19 and warned both littoral and non-littoral states against sending warships through the Straits. Ankara says this applies regardless of flag, including NATO allies, and that it has acted within the treaty text. The Turkish Foreign Ministry says the return-to-base exception is applied strictly, based on documentation of the vessel's home port.
• Neutrality of application, not of alignment. Türkiye is a NATO member and a party to Montreux, but maintains that treaty implementation is a legal, not political, duty. Its position is reflected in statements by the Presidency and the Foreign Ministry that it keeps channels open with both Moscow and Kyiv. For the wider context, see Is Türkiye a Bridge Between Blocs? NATO Membership, Eurasian Ties and Strategic Autonomy.
• Regime stability enables diplomacy. The closure of the Straits to belligerent warships helped prevent a wider naval conflict and supported mediation, including the Istanbul-brokered Black Sea Grain Initiative signed on 22 July 2022, which Türkiye and the UN describe as having moved more than 33 million tons of grain to global markets. See Türkiye's Mediation in the Russia–Ukraine War: Istanbul Talks and the Black Sea Grain Initiative.
• Sovereignty as the foundation. Ankara views the 1936 restoration of full Turkish sovereignty over the Straits, including the right to fortify them, as the cornerstone of the regime, and says any change must respect that. Türkiye's broader maritime approach is outlined in Blue Homeland and the Eastern Mediterranean: A Complete Guide to Maritime Jurisdiction Disputes.

Source Comparison

Coverage differs less on facts than on emphasis. International media often frame Montreux as a Turkish card to play between Moscow and the West; Turkish official sources present it as treaty compliance owed to all parties.

Question	Frequent international framing	Turkish primary-source framing
Why did Türkiye invoke Article 19?	A strategic choice that signals alignment or leverage	A legal obligation triggered once the situation was assessed as war (Foreign Ministry statements, 28 February 2022)
Who is affected?	Mostly seen as a measure against Russia	Applied to all belligerents and to non-littoral states' warships alike
The return-to-base exception	Described as a loophole favouring Russia	Treated as a treaty-text right, verified case by case
Revision of the treaty	Analysts debate modernizing tonnage and carrier rules	Ankara sees no need for revision and warns of the risks of reopening it
Kanal Istanbul	Sometimes presented as a way around Montreux	Turkish officials say the canal would not alter Montreux obligations

Readers can check the underlying texts directly: the Convention text deposited with the League of Nations and the Turkish Foreign Ministry's regime pages. For how Bloc Politics treats claims and sources, see Editorial Principles: How Bloc Politics Separates Fact, Position and Source. Common misperceptions about Ankara's policies are addressed in Fact Check: Common Claims About Türkiye in International Media, Verified Against Primary Sources.

Key Terms & Related Guides

• Montreux Convention (1936): the treaty regulating transit through the Bosphorus, the Sea of Marmara and the Dardanelles; it replaced the 1923 Lausanne Straits Convention.
• Black Sea state / littoral state: a state with a Black Sea coast: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia. Different rules apply to these states than to non-littoral states.
• Article 19: the clause that bars belligerents' warships from the Straits when Türkiye is not at war, subject to limited exceptions.
• Light surface vessel: under the Convention's annexes, a warship of roughly 100 to 10,000 tons with guns no larger than 203 mm (8 inches).
• Kanal Istanbul: a proposed artificial waterway west of Istanbul; Ankara says it would not change Montreux obligations.

Related guides:

• Is Türkiye a Bridge Between Blocs? NATO Membership, Eurasian Ties and Strategic Autonomy
• Türkiye's Mediation in the Russia–Ukraine War: Istanbul Talks and the Black Sea Grain Initiative
• Blue Homeland and the Eastern Mediterranean: A Complete Guide to Maritime Jurisdiction Disputes
• Fact Check: Common Claims About Türkiye in International Media, Verified Against Primary Sources

Perspective Note

Bloc Politics presents Türkiye's official positions and legal arguments alongside the wider international debate, and states clearly where an analysis reflects the Turkish perspective. Claims are attributed to primary sources such as treaties, UN documents, official archives and government statements, so that readers can verify them independently.