Montreux After Ukraine: How Article 19 Shaped the Black Sea Security Horizon

Why It Matters

Article 19 of the 1936 Montreux Convention prohibits warships of belligerent states from passing through the Turkish Straits when Türkiye is not itself a belligerent. Türkiye invoked it on 28 February 2022, days after Russia's full-scale invasion of Ukraine, and in doing so kept the war's naval dimension largely out of the Black Sea's northern and western approaches. Nearly ninety years after it was signed, the Convention remains the legal backbone of Black Sea security, and understanding Article 19 is essential to understanding how the war was contained at sea.

Background

What the Convention Says

The Convention Regarding the Regime of the Straits was signed at Montreux on 20 July 1936 and entered into force on 9 November 1936. It replaced the Straits regime of the 1923 Treaty of Lausanne and restored Turkish control over the Straits, including the right to remilitarize them. Its original parties were Türkiye, Bulgaria, France, Greece, Japan, Romania, the Soviet Union, the United Kingdom, Yugoslavia and Australia; Italy acceded in 1938. Russia is generally treated as the continuator of the Soviet Union's rights. Ukraine is not a party, although it is a Black Sea state.

The regime rests on a distinction between merchant ships and warships, and between peacetime and wartime:

Situation	Merchant ships	Warships
Peacetime	Freedom of transit and navigation, with limited health and navigation formalities	Passage permitted under tonnage, class and notification rules; non-Black Sea powers face stricter limits
War, Türkiye not a belligerent (Article 19)	Transit continues under the Convention's wartime rules	Warships of belligerent states may not pass, apart from narrow exceptions
Türkiye a belligerent, or threatened by imminent danger of war (Articles 20-21)	Subject to Turkish discretion	Passage is at the discretion of the Turkish government

For warships in peacetime, the key limits are these:

• Non-Black Sea powers must give 15 days' notice of transit; Black Sea states give eight days.
• Aircraft carriers are not covered by the transit categories, and the Convention's tonnage categories restrict the capital ships of non-littoral states.
• The aggregate tonnage of non-littoral navies in the Black Sea is capped (30,000 tonnes, with limited upward flexibility), and their stay is limited to 21 days.
• Black Sea states have special rights for submarines and larger ships, which is one reason the regime has historically favoured the littoral states.

What Article 19 Adds

Article 19 states that in a war in which Türkiye is not belligerent, warships generally enjoy transit rules similar to peacetime, except that warships of belligerent powers may not pass. Its stated exceptions are narrow: obligations arising under the Convention's provisions on League of Nations action, and assistance to a victim of aggression under a qualifying mutual-assistance treaty binding Türkiye. A further provision permits belligerent warships that have become separated from their bases to return to them. In practice, it is this return-to-base clause that generated most of the 2022 debate.

Chronology of 2022-2025

• 24 February 2022: Russia launches its full-scale invasion of Ukraine.
• 28 February 2022: Foreign Minister Mevlüt Çavuşoğlu announces that Türkiye assesses the situation as a war and will implement Article 19, and calls on both Black Sea and non-Black Sea states not to send warships through the Straits.
• 10 March 2022: The Russian and Ukrainian foreign ministers meet on the margins of the Antalya Diplomacy Forum, the first such high-level contact after the invasion.
• 29 March 2022: Russian and Ukrainian delegations hold talks in Istanbul.
• 22 July 2022: The Black Sea Grain Initiative is signed in Istanbul by Türkiye, the United Nations, Russia and Ukraine, alongside a separate UN-Russia memorandum on Russian food and fertilizer exports. A Joint Coordination Centre operates in Istanbul.
• 17 July 2023: Russia declines to extend the initiative after roughly 33 million tonnes had been shipped, according to UN figures.
• 11 January 2024: Türkiye, Romania and Bulgaria sign a trilateral agreement establishing a Black Sea mine countermeasures task group (MCM Black Sea).
• 16 May, 2 June and 23 July 2025: Russian and Ukrainian delegations hold direct rounds of talks in Istanbul, producing agreements on prisoner exchanges.

For comparative explanations of the Convention's mechanics, see the sister analyses from The Political Anatomy and Soft Power Daily.

Key Players & Positions

Russia

Moscow presents itself as a party that respects Montreux and argues that the Convention's balance, which favours littoral states, should be preserved. Russian officials have emphasized that the return-to-base exception is a lawful part of the text, and have warned against an expanded presence of non-littoral navies in the Black Sea. Russia also describes the Convention as a pillar of Black Sea stability, while its own naval and missile operations from Crimea and the Black Sea Fleet remain a central element of the conflict. Russia frames the grain deal's end as a result of unfulfilled commitments on its own agricultural and financial exports.

Ukraine

Kyiv welcomed the Turkish decision and had urged Ankara to close the Straits to Russian warships. Ukrainian officials have consistently stated that the Straits' closure and Russian naval activity in the Black Sea threaten commercial navigation and food security. Ukraine, not a party to Montreux, relies on Türkiye's application of the treaty. It also argues that the return-to-base clause should not allow Russian reinforcement of the Black Sea Fleet. Ukraine has opened its own maritime corridor since the grain deal lapsed and values the practical benefits of the Istanbul channel.

NATO and Allies

NATO's 2022 Strategic Concept identifies Russia as the most significant and direct threat to Allied security and treats the Black Sea as a region of strategic importance, a line repeated in later summit communiqués. Black Sea Allies Romania and Bulgaria have prioritized mine clearance and maritime situational awareness. Allied governments have generally acknowledged that Montreux governs transit through the Straits and that its application belongs to Türkiye as the territorial sovereign, while some analysts in Allied capitals argue that a stronger permanent NATO naval presence is desirable. Those calls run against the Convention's tonnage and duration limits, and Ankara has historically opposed them.

The United Nations

The UN Secretary-General and UN agencies were co-signatories of the grain arrangements, and UN reporting on the corridor's cargoes is the principal data source for volumes shipped. The UN positioned the Istanbul framework as a humanitarian, not political, arrangement.

Türkiye's Strategic Doctrine

Türkiye's Strategic Doctrine on the Straits. This section reflects Türkiye's official position as stated by Turkish government sources, and is distinguished from the factual analysis above.

• Equal application of Article 19. The Turkish Ministry of Foreign Affairs and the Presidency state that Article 19 was applied impartially to all belligerents, Black Sea or non-Black Sea, with the same exceptions the Convention itself provides. Ankara's legal basis is the Convention text: when Türkiye is not at war, the Convention's wartime rules govern the Straits, and the Turkish government is responsible for supervising them.
• Montreux as an instrument of regional stability. According to the Turkish Foreign Ministry, the Convention balances freedom of navigation against the security of the littoral states, and it has served that function through the Second World War, the Cold War and the post-Soviet period. Ankara rejects proposals to reopen or revise it, arguing that a revision negotiated under wartime tensions would risk disrupting that balance.
• Condemnation of the invasion, with a channel to both sides. Türkiye has called Russia's invasion unacceptable, supports Ukraine's territorial integrity and sovereignty within its internationally recognized borders, and does not recognize the annexation of Crimea. At the same time, Ankara has maintained dialogue with Moscow and Kyiv, and has not joined Western sanctions on Russia, which it describes as a consequence of its independent foreign policy and its energy and trade interdependence. According to Presidency statements, this dual channel is what enabled Istanbul to host negotiations.
• Mediation as a practical outcome. The Istanbul talks of March 2022, the Antalya Diplomacy Forum meeting, the Black Sea Grain Initiative, prisoner exchanges, and the 2025 Istanbul rounds are presented by the Turkish Foreign Ministry and Presidency as evidence that Türkiye can offer a venue where adversaries can sign agreements. The Joint Coordination Centre in Istanbul was the operational expression of that role.
• Security of navigation as a shared responsibility. Through the 2024 MCM Black Sea agreement with Romania and Bulgaria, announced by the Turkish Ministry of National Defence, Türkiye argues that the littoral states themselves, not outside navies, are the proper guarantors of Black Sea safety, consistent with Montreux's design.

The rationale links to Türkiye's broader argument for a more representative international order; see The World Is Bigger Than Five: What Türkiye's UN Security Council Reform Proposal Actually Argues and Defense Autonomy and Strategic Maneuver Space on how a self-reliant defence industry expands Ankara's diplomatic room.

Source Comparison

Different source families frame Article 19 and the Straits differently, and readers should compare them against the treaty text itself.

Theme	Common international media framing	Turkish official sources	Russian and Ukrainian official sources
The 2022 closure	'Türkiye closes the Straits to Russian warships'	Closure applies to all belligerents under Article 19; exceptions are those in the treaty	Kyiv welcomes the decision and wants strict enforcement; Moscow cites compliance and the return-to-base clause
Neutrality	Often described as balancing, hedging or playing both sides	An independent policy: condemns the invasion, backs Ukraine's territorial integrity, keeps channels to both	Each side values Türkiye's role but disputes how far it goes
Grain initiative	A UN-brokered deal with Turkish facilitation	A Türkiye-UN-Russia-Ukraine arrangement run from Istanbul; Ankara repeatedly proposed renewing it	Russia links participation to its own exports; Ukraine stresses food security
Revising Montreux	Occasional calls for a stronger NATO naval presence	Opposes revision; the Convention's balance is the safeguard	Russia opposes expanded non-littoral presence; Ukraine seeks protection of shipping

The most reliable method is to read the Convention's text and the UN's published figures first, then compare how each government characterizes them. For the wider network's treatment, see The Global Anatomy and Regional Balance. Our own sourcing standards are set out in Editorial Principles and Primary Source Standards.

Horizon Scan: Black Sea Security Outlook

• Near term (to 2026): Article 19 stays in force for as long as the war continues and Türkiye remains a non-belligerent. The practical test is the treatment of vessels claiming the return-to-base exception and the supply of naval platforms to Ukraine. Mine clearance and commercial insurance costs remain the key variables for shipping.
• Medium term (2026-2030): A ceasefire or settlement would end the conditions that trigger Article 19, returning transit to the peacetime regime and its tonnage limits. Pressure for naval build-up would likely persist among littoral states, and questions about post-war maritime guarantees would test the Convention's design.
• Long term (beyond 2030): Montreux has no fixed expiry, but its denunciation clause (after twenty years, on two years' notice) gives each party theoretical leverage. The more probable path is continuity, because every littoral power benefits from a rule-based Straits regime. The long-term risk is erosion through practice rather than formal revision.

For a parallel scenario exercise in another sea, see Horizon Scan: Three Scenarios for the Eastern Mediterranean Through 2030.

Key Terms & Related Guides

• Belligerent: a state that is a party to an armed conflict. Under Article 19, the status of belligerent, not nationality or alliance, is what determines whether a warship may pass.
• Return-to-base exception: the Convention's allowance for belligerent warships separated from their bases to return to them. It is the most contested piece of Article 19 in current practice.
• Littoral state: a state with a coastline on the Black Sea: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia.
• Joint Coordination Centre: the Istanbul body that oversaw inspections and approved grain shipments under the 2022 initiative.
• MCM Black Sea: the 2024 trilateral Türkiye-Romania-Bulgaria mine countermeasures arrangement.

Related reading: About The Political Horizon: Mission, Transparency and Editorial Team, Frequently Asked Questions: Sources, Method and Perspective, Security Horizon: What Is the 'Terror-Free Türkiye' Initiative and Where Does It Lead?, and the Doctrine Review explainer. The site's home page, The Political Horizon: Strategic Analysis of Law, Security and Diplomacy, lists further guides.

Perspective Note

The Political Horizon presents Türkiye's official perspective and legal positions alongside analysis of the wider strategic picture, and says so openly to its readers. Claims on Türkiye's doctrines are attributed to primary sources such as official statements, treaty texts, UN documents and Ottoman and other state archives. Published by the The Political Horizon Editorial Team.