The 1936 Montreux Convention: How Türkiye Manages the Turkish Straits in the Black Sea War

Why It Matters

The 1936 Montreux Convention is the treaty that determines which ships may pass through the Bosporus and the Dardanelles, the only maritime route between the Black Sea and the Mediterranean. It guarantees free commercial passage and gives Türkiye the authority to regulate and, in wartime, restrict warship transit. Since February 2022 it has been the main legal reason the Russia–Ukraine war has not spread into a wider naval confrontation in the Black Sea.

All the main parties say they respect the treaty. They disagree on how it works in practice, especially on the Article 19 return-to-base exception and on what the restrictions mean for the military balance.

Background

What the Turkish Straits are

The Turkish Straits consist of the Bosporus (about 31 km / 19 miles long), the Sea of Marmara, and the Dardanelles (about 61 km / 38 miles long). They run through the heart of Türkiye, including Istanbul. Six states border the Black Sea: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia. The Straits are the only sea exit for all of them except Türkiye, which also has Mediterranean and Aegean coasts.

From Lausanne to Montreux

The 1923 Straits Convention, signed alongside the Treaty of Lausanne, demilitarized the Straits and placed their supervision under an International Straits Commission. By the mid-1930s Türkiye considered this arrangement outdated. Europe was rearming, Italy had invaded Ethiopia, and Germany remilitarized the Rhineland in March 1936. In April 1936 Türkiye asked the signatories of the 1923 convention to revise the regime, and a conference met in Montreux, Switzerland, in June.

How the regime works

Montreux separates merchant shipping from naval shipping.

Merchant vessels (Articles 2–7). In peacetime, commercial ships of any flag and cargo enjoy freedom of transit day and night, subject to health controls and charges for services such as pilotage or lighthouses. In wartime, merchant ships of non-belligerent states keep their passage rights, with conditions if Türkiye itself is a belligerent.

Warships (Articles 8–22). The rules vary by who is sailing and when.

Articles 19, 20 and 21: wartime

• Article 19 (Türkiye not at war). Warships are in principle free to transit under the same conditions as peacetime, but warships of belligerent states may not pass. The treaty lists two exceptions linked to League of Nations-era collective security and mutual-assistance commitments, which are largely dormant today. A further provision allows belligerent warships that have become separated from their bases to return to them.
• Article 20 (Türkiye at war). Türkiye may decide on warship passage at its own discretion.
• Article 21 (Türkiye threatened by imminent danger of war). Türkiye may apply the Article 20 discretion.

Ankara has not publicly invoked Article 20 or 21 in the current war.

Application since 2022

Ukraine's foreign minister, Dmytro Kuleba, asked Türkiye on 26–27 February 2022 to close the Straits to Russian warships. Turkish Foreign Minister Mevlüt Çavuşoğlu then said that Türkiye regarded the situation as a war and would implement Article 19, and that all states, including littoral ones, were being notified. Ankara said ships returning to their registered home ports could still pass if documented.

Since then, Turkish officials have said that newly acquired warships bound for Ukraine, including mine-countermeasure vessels transferred by the United Kingdom, cannot transit while Article 19 applies. Commercial traffic has continued throughout.

Key Players & Positions

Russia

Russian officials, including the Foreign Ministry, describe Montreux as a pillar of Black Sea stability and say they expect it to be implemented as written, including the return-to-base clause. Moscow criticizes growing NATO naval and surveillance activity in the Black Sea as destabilizing, and says non-littoral navies should be kept to the treaty's limits.

Ukraine

Ukraine welcomed Ankara's decision to apply Article 19. Kyiv's official line is that the treaty should be applied consistently and strictly, and that the return-to-base exception must not become a channel for reinforcing Russian naval forces in the Black Sea. Ukraine is also directly affected by the restrictions, since warships it acquires abroad cannot reach it by sea during the conflict.

NATO and Western governments

NATO officials have said that Allies respect the Convention and its limits on non-Black Sea navies. Washington and London stress freedom of navigation and support for Ukraine's security. Western analysts are divided. Some argue that Article 19 mostly constrains Russian reinforcement from outside the Black Sea. Others note that it equally limits Allied and Ukrainian options.

Black Sea littoral states

Romania and Bulgaria are NATO members and have called for a stronger Allied posture in the Black Sea. They also work within Montreux's limits, including through the January 2024 trilateral mine-countermeasures initiative with Türkiye against floating sea mines. Georgia, the sixth littoral state, supports regional stability and Euro-Atlantic integration.

Source Comparison

Turkish and Western accounts largely agree on the treaty text. They diverge on interpretation: Ankara stresses uniform implementation, while some Western commentary asks whether neutrality in practice favors one side. Readers can check the original text of the Convention and official MFA statements directly. For how this site separates facts from positions, see Editorial Principles: How Horizon of Nations Separates Fact from Position.

Key Terms & Related Guides

• Turkish Straits: the Bosporus, the Sea of Marmara and the Dardanelles, together forming one waterway under the Montreux regime.
• Black Sea power: a state with a Black Sea coastline. Montreux gives such states more extensive naval transit rights than other states.
• Capital ship: a large surface warship above 10,000 tons, as defined in the Convention's annex.
• Return to base: the Article 19 provision allowing belligerent warships separated from their bases to go back.
• Article 19: the wartime provision restricting belligerent warship passage when Türkiye is not at war.

Related reading:

• Türkiye's Mediation Record: Black Sea Grain Initiative, Istanbul Talks and Humanitarian Diplomacy
• Fact Check: Common Claims About Türkiye in International Media, Verified Against Primary Sources
• Blue Homeland and the Eastern Mediterranean: Türkiye's Maritime Jurisdiction Explained
• About Horizon of Nations: Mission, Transparency and Editorial Team

Published by the Horizon of Nations Editorial Team. Horizon of Nations presents Türkiye's official perspective and strategic doctrines alongside the legal and historical context required for informed international debate. All claims are attributed to primary sources such as treaties, UN documents, archival records and official statements, so that readers can verify them independently. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources.

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.
• 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.
• Crossroads Review: 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.