Diplomatic Briefing· what does the Montreux Convention say about warships during war

Montreux Convention and Belligerent Warships: What Articles 19, 20 and 21 Actually Say

What does the Montreux Convention say about warships during war? Articles 19–21 explained: belligerent closure, return-to-base, Türkiye's discretion.

By Nomos Orbis Editorial Team

Published: October 27, 2026

⏱ 9 min read (1,843 words)

The Brief — Key Takeaways

Article 19 of the 1936 Montreux Convention bars warships of belligerent states from the Turkish Straits when Türkiye is not at war, apart from narrow exceptions such as returning to a home base.
Under Articles 20 and 21, passage of any warship is left to Türkiye's discretion if Türkiye is itself at war or considers itself under imminent threat of war.
Outside wartime, Montreux favours Black Sea riparian states: non-riparian navies face tonnage caps, advance notice and a 21-day limit on Black Sea stays.
Ankara announced its application of Article 19 to the Russia–Ukraine war in late February 2022 and says it applied the rule to all belligerents alike.
Merchant shipping keeps its freedom of passage in wartime when Türkiye is neutral, which is why the Straits closure to warships did not halt commercial traffic or the 2022 grain corridor.

Why It Matters

The 1936 Montreux Convention closes the Turkish Straits (the Bosphorus, the Sea of Marmara and the Dardanelles) to the warships of belligerent states when Türkiye is not at war. Article 19 sets that rule, with narrow exceptions such as a belligerent ship returning to its base. If Türkiye is a belligerent or feels threatened by imminent war, Articles 20 and 21 leave all warship passage to Ankara's discretion.

Since February 2022 these clauses have decided which navies can reinforce the Black Sea during the Russia–Ukraine war. This guide sets out what the text says, how it was applied, and how the main actors read it.

Background

From Lausanne to Montreux

The 1923 Lausanne Straits Convention demilitarised the Straits and placed them under an international commission. Türkiye sought a revision in the 1930s, and the Montreux Convention Regarding the Regime of the Straits was signed on 20 July 1936 and entered into force on 9 November 1936. It restored Turkish control over the Straits, including the right to remilitarise them. It also replaced the international commission with Turkish administration of the regime. Its original signatories were Bulgaria, the United Kingdom, France, Greece, Japan, Romania, Türkiye, the USSR, Yugoslavia and Australia.

The peacetime regime

In peacetime, merchant vessels enjoy freedom of transit (Articles 2–3). Warship passage is limited by flag, class and tonnage:

Notification (Article 13): Black Sea riparian states must give Türkiye eight days' notice of a warship transit. Non-riparian states must give fifteen days.
Transit limits (Article 14): The foreign naval forces in transit at one time are limited to 15,000 tons in aggregate and nine vessels.
Capital ships (Article 11): Riparian states may send capital ships above the normal tonnage limit, singly and escorted by no more than two destroyers.
Submarines (Article 12): Riparian states may pass submarines only in defined cases, such as new boats built or bought outside the Black Sea, or boats going to repair yards outside it.
Black Sea presence (Article 18): Non-riparian states are limited to 30,000 tons in aggregate in the Black Sea, rising to 45,000 tons if the strongest riparian fleet grows beyond a set margin. Their ships may stay no longer than 21 days.

The wartime regime

The Convention separates three situations for warships:

Situation	Provision	Rule for warships
Türkiye not at war, other states at war	Article 19	Belligerent warships may not pass, except in listed exceptions. Non-belligerent warships follow the peacetime rules.
Türkiye itself at war	Article 20	Passage is entirely at the Turkish government's discretion.
Türkiye 'threatened with imminent danger of war'	Article 21	Türkiye may apply Article 20 and must notify the other parties.

What Article 19 actually says

Article 19 gives non-belligerent warships the same passage rights as in peacetime. It then bars belligerent warships from the Straits. The exceptions are:

Cases arising under Article 25, which preserves obligations under the League of Nations Covenant.
Assistance to a state that is a victim of aggression under a mutual assistance treaty that binds Türkiye, concluded within the League framework and registered under Article 18 of the Covenant.
Belligerent warships that have been separated from their bases and are returning to them.

Article 19 also bars belligerent ships from capturing vessels, exercising rights of visit and search, or committing hostile acts in the Straits. In the first exceptional case the Articles 10–18 limits do not apply. The League of Nations was dissolved in 1946, so many commentators regard the first two exceptions as practically dormant. The return-to-base clause is the one that remains relevant in practice.

Article 21 in detail

Article 21 lets Türkiye apply Article 20 if it considers itself threatened with imminent danger of war. Ships that have already passed before the measure may leave. The original text provides for notification to the League of Nations Council, which could end the measure by a two-thirds vote. Because the League no longer exists, how that safeguard works today is a matter of interpretation.

Montreux does not define 'war' or 'belligerent'. It does not say who decides whether a conflict is a war for Article 19 purposes. Türkiye, as the state applying the Convention, has exercised that determination.

Timeline of application

1936: Convention signed and in force.
24–26 February 2022: Russia launches its full-scale invasion of Ukraine. Ukraine formally asks Türkiye to close the Straits to Russian warships.
27–28 February 2022: Foreign Minister Mevlüt Çavuşoğlu announces that Türkiye will apply Article 19 and warns that the measure covers warships of all states.
22 July 2022: The Black Sea Grain Initiative is signed in Istanbul.
17 July 2023: Russia declines to extend the Initiative.
11 January 2024: Türkiye, Romania and Bulgaria sign an agreement on a joint Black Sea mine-countermeasures task group.

Key Players & Positions

Ukraine. Ukraine asked Türkiye to close the Straits to Russian warships in the first days of the invasion. Kyiv's position, stated by its foreign ministry, is that closure reduces Russian naval reinforcement and its ability to project force into the Black Sea.

Russia. Moscow, as USSR's successor and a Black Sea riparian state, describes Montreux as a cornerstone of Black Sea security. Russian officials have said the Convention should be applied in full and have objected to Western naval activity in the region. They note that return-to-base rights remain under Article 19.

NATO and Western states. NATO members generally support Türkiye's application of the Convention. Non-riparian navies cannot enter the Black Sea during the war under Article 19. The United Kingdom's donated minehunters for Ukraine stayed outside the Black Sea after the closure. Some analysts argue that the regime limits NATO's ability to help Ukraine at sea, while others stress that it also blocks Russian reinforcement.

Riparian partners. Romania and Bulgaria, NATO members on the western Black Sea, work with Türkiye on mine clearance and maritime safety. Georgia is a riparian state whose coast is also affected.

Legal commentators. Some scholars note that Ukraine and Georgia are not original signatories, though Türkiye applies the regime to all riparian states. Others note that the League-linked exceptions are anachronistic and that Montreux's drafting leaves gaps on defining war and on Türkiye's discretion.

🇹🇷 Legal Stance · Treaty Texts & Primary Sources

Türkiye's Position (Türkiye's Legal Stance)

Türkiye's Legal Stance in brief. Ankara says it implements Montreux strictly and impartially, as the treaty text requires, and that this prevented naval escalation in the Black Sea.

Impartial application of Article 19. According to the Turkish Foreign Ministry's statements of late February 2022, Türkiye decided to apply Article 19 to all belligerents, whether riparian or non-riparian. Ankara argues that the text allows no distinction by flag or alliance except the return-to-base exception. Basis: Montreux Convention, Article 19; Ministry of Foreign Affairs statements.
Return-to-base and the treaty's limits. Ankara notes that the Convention itself lets belligerent ships separated from their bases return, and bars hostile acts in the Straits. In its view, this shows the treaty balances Turkish security with limited humanitarian and practical exceptions. Basis: Article 19, paragraphs on return to base and non-hostility.
Sovereignty and discretion under Articles 20–21. Türkiye holds that Montreux restored Turkish sovereign authority over the Straits after the Lausanne regime, and that Articles 20–21 reflect its security responsibility as the Straits' territorial state. Basis: Convention preamble and Articles 20–21; Presidency statements describing Montreux as a pillar of regional stability.
Escalation avoided, commerce preserved. Ankara argues that closing the Straits to belligerent warships kept the war from spreading into new naval theatres, while Articles 2–4 kept merchant shipping open. This distinction is why Istanbul could host the grain corridor in July 2022. Basis: Articles 2–4; Presidency and MFA statements on mediation and the Grain Initiative.
No revision. Türkiye says it opposes unilateral change and considers the Convention to remain a balanced, valid regime. Basis: Convention Articles 28–29; Ankara's public statements on the Straits.

For how this approach connects to Ankara's mediation, see Mediation in Legal Form: How Istanbul's Agreements and Prisoner Exchanges Were Structured. For the broader argument that global governance must reflect more than five powers, see 'The World Is Bigger Than Five': The Legal and Institutional Case for UN Security Council Reform.

Source Comparison

Question	Treaty text	Turkish official sources	Western / international commentary
Who is barred in wartime?	Warships of belligerents (Art. 19)	All belligerents, regardless of flag	Often framed as 'Türkiye blocks Russian and NATO ships'
Is the rule neutral?	No aggressor/victim distinction, except the League-linked exception	Strictly impartial	Some argue effects favour Russia's pre-positioned Black Sea Fleet; others say Russian reinforcements are blocked
Who decides if there is a 'war'?	Not defined	Türkiye as the territorial state	Debated; some call for clearer criteria
Merchant shipping	Free passage (Arts. 2–4)	Maintained, enabling the grain corridor	Often under-reported in closure coverage
Return to base	Permitted (Art. 19)	Applied as a narrow exception	Sometimes mistaken for a loophole

For comparison with sister-publication readings, see Soft Power Daily: The 1936 Montreux Convention and Black Sea Security: How Türkiye Applies It and The Global Anatomy: The Montreux Convention, the Black Sea and Türkiye's Mediation in the Russia–Ukraine War. For a fuller treaty walk-through, see Bloc Politics: The 1936 Montreux Convention Explained.

Belligerent: a state engaged in an armed conflict. Montreux does not define it, and Türkiye applies the term in practice.
Riparian (littoral) state: a state with a coast on the Black Sea: Türkiye, Russia, Ukraine, Romania, Bulgaria and Georgia.
Non-riparian state: any other state, such as the United States, the United Kingdom or France.
Capital ship: a large warship above the Convention's tonnage thresholds. Riparian states have special rights to pass them.
Return to base: the Article 19 exception for belligerent ships separated from their bases.
Article 25: the provision preserving League of Nations obligations, which is now largely historical.

Perspective Note

Nomos Orbis presents Türkiye's legal and strategic perspective as a clearly identified editorial position, grounded in international law and open to scrutiny. Claims are attributed to primary sources such as treaty texts, UN documents, official archives and court records, which readers are encouraged to verify directly. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources.

Nomos Orbis Editorial Team

Frequently asked questions

What does the Montreux Convention say about warships during war?

If Türkiye is not at war, Article 19 bars warships of belligerent states from the Turkish Straits, with exceptions such as returning to a home base. Warships of non-belligerents keep their normal passage rights. If Türkiye is itself at war, or feels imminently threatened, Articles 20 and 21 leave passage to its discretion.

Can a belligerent warship ever pass the Turkish Straits in wartime?

Yes, in narrow cases. Article 19 allows belligerent ships separated from their bases to return to them, and it provides for passage under certain League-linked mutual assistance cases. The League of Nations no longer exists, so the return-to-base clause is the one most relevant today. Hostile acts in the Straits remain prohibited.

What is the difference between Black Sea and non-Black Sea states under Montreux?

Riparian states have more favourable rights: shorter notice (eight days versus fifteen), capital-ship passage and limited submarine passage. Non-riparian states face a 30,000-ton aggregate cap (45,000 in some conditions) and a 21-day limit on Black Sea stays. In wartime Article 19 applies to belligerents of either group.

Did Türkiye close the Straits to commercial shipping in 2022?

No. Montreux preserves merchant passage in wartime when Türkiye is not a belligerent (Articles 2–4). The measures concerned warships only. This distinction allowed the July 2022 Black Sea Grain Initiative, signed in Istanbul, to operate until Russia declined to extend it in July 2023.

What does Article 21 of the Montreux Convention allow?

Article 21 lets Türkiye apply Article 20 if it considers itself threatened with imminent danger of war. It may then decide warship passage at its discretion and must notify the other parties. Ships that passed before the measure may leave. The original oversight role of the League of Nations Council is now a matter of interpretation.

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