Montreux Article 19 in Practice: How Türkiye Closed the Straits to Warships During the Ukraine War

Why It Matters

Article 19 of the 1936 Montreux Convention is the clause that lets Türkiye keep the warships of belligerent states out of the Bosphorus and the Dardanelles when a war is under way and Türkiye is not a party to it. Since late February 2022 Ankara has applied it to the war in Ukraine, which means the Turkish Straits have worked as a legal gate, a soft border, between the Mediterranean and a Black Sea war zone. The rule is short, but its exceptions and its interpretation are contested by Russia, Ukraine and several NATO members, and this guide sets out what the text says and how each side reads it.

Background

From Lausanne to Montreux

The 1923 Lausanne Straits Convention demilitarised the Straits and placed them under an international commission. Türkiye sought revision in the 1930s as security conditions worsened. The Montreux Convention was signed on 20 July 1936 and entered into force on 9 November 1936. It restored Turkish sovereignty over the Straits, allowed remilitarisation, and transferred the commission's functions to the Turkish government. For the wider treaty framework, see Borders Drawn by Treaty: How Lausanne, Kars and Montreux Shape Türkiye's Frontiers.

The regime covers the Dardanelles, the Sea of Marmara and the Bosphorus. It balances two aims: freedom of commercial navigation, and limits on the naval presence of states that do not border the Black Sea.

The peacetime regime

In peacetime the convention treats merchant and naval traffic very differently:

• Merchant vessels enjoy freedom of transit and navigation by day and night, whatever their flag or cargo (Articles 1 and 2). Türkiye may levy only the sanitary, lighthouse and similar charges the convention lists.
• Warships of Black Sea states may transit with advance notification. Black Sea states may send capital ships above 15,000 tons only singly and escorted by no more than two destroyers (Article 11), and may send submarines only in limited circumstances such as return from construction or repair (Article 12).
• Warships of non-Black Sea states face limits on tonnage, number and duration of stay. Notification periods are 8 days for Black Sea states and 15 days for others (Article 13). Aggregate tonnage in the Black Sea is capped and the stay may not exceed 21 days (Article 18). Aircraft carriers are not covered by the transit regime.

These limits are the reason the Black Sea has never hosted a standing non-littoral fleet.

The wartime provisions

The convention sets out three distinct wartime scenarios:

1. Türkiye is at war (Article 20). The peacetime limits on warships no longer bind, and Türkiye has discretion over passage.
2. Türkiye considers itself threatened with imminent danger of war (Article 21). Türkiye may apply the same discretion and must notify the other parties.
3. A war occurs and Türkiye is not belligerent (Article 19). This is the scenario that applies to the war in Ukraine.

What Article 19 says

Under Article 19, warships generally enjoy transit in wartime on the peacetime terms, but vessels of belligerent powers may not pass through the Straits. The text lists three exceptions:

• cases arising from Article 25, which preserves Türkiye's obligations under the League of Nations Covenant (read today in the context of the UN Charter);
• assistance to a victim of aggression under a mutual-assistance treaty binding Türkiye, concluded within the League framework and registered under Article 18 of the Covenant;
• belligerent warships that have become separated from their bases, which may return to them.

The article also forbids belligerent warships from making captures, exercising visit and search, or committing any hostile act in the Straits.

Chronology of the 2022 application

Many analysts treat the 2022 invocation as the first major wartime application of the Article 19 mechanism since the Second World War, when Türkiye was also non-belligerent for most of the conflict. For comparison with sister-publication analyses, see The Political Anatomy on Montreux, Article 19 and Black Sea security and Soft Power Daily on how Türkiye applies the convention.

Key Players & Positions

Ukraine. Foreign Minister Dmytro Kuleba publicly asked Türkiye to close the Straits to Russian warships in the first days of the invasion. Kyiv has welcomed Ankara's application of Article 19 and has argued that the return-to-base exception should not become a loophole that lets an aggressor reinforce its Black Sea operations.

Russia. Moscow says it respects the convention and that Türkiye is acting within its sovereign rights. Russian officials have criticised the NATO naval presence and Western arms deliveries in the region and have emphasised that the return-to-base clause is part of the treaty text. Russia's Black Sea Fleet is based inside the Black Sea, so the closure mainly constrains reinforcement from other fleets.

NATO members. Allied governments, including the United States and the United Kingdom, have said they respect Montreux and Türkiye's role as its custodian. Black Sea allies Romania and Bulgaria have an interest in limiting escalation and in demining; they cooperate with Türkiye in the 2024 mine countermeasures arrangement. Some allies have sought wider Black Sea naval access, but the convention's tonnage and duration limits apply to them in peacetime, and Article 19 applies to them if they become belligerents.

Interpretation debate. Commentators disagree on several points:

• whether Türkiye needs a formal finding or declaration that a war exists, or whether it holds a margin of appreciation;
• how widely the return-to-base exception should be read, including whether it covers ships that were never separated by the war itself;
• whether new deliveries of warships from shipyards to a belligerent are caught by the Article 19 bar;
• whether the League-era references in Articles 19 and 25 map neatly onto the UN Charter.

The text gives Türkiye, as the territorial sovereign, the practical task of deciding these cases.

Source Comparison

A useful habit when reading coverage is to check the convention text against the claim. Our Primary-Source Checklist and the Editorial Principles explain how we do this. For parallel treatments, see The Global Anatomy on Montreux and Türkiye's mediation.

Key Terms & Related Guides

• Belligerent: a state that is a party to an armed conflict. Article 19 turns on this status.
• Non-riparian / non-littoral state: a state without a Black Sea coastline. Montreux gives such states fewer naval transit rights in peacetime.
• Return to base: the clause allowing belligerent warships separated from their home bases to go back to them.
• Capital ship: in the convention, a large surface warship with a tonnage above the thresholds set for the transit regime.
• Straits: the Dardanelles, the Sea of Marmara and the Bosphorus, regulated together under Montreux.

Related reading: The Southern Border: How Türkiye Secures Its 1,300 km Line with Syria and Iraq for Türkiye's land frontier, Where Does Türkiye's Maritime Border Begin? for its maritime lines, and About The Soft Border for our mission and perspective.

The Soft Border presents global and regional affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy and legal doctrines as stated by Turkish primary sources.