Black Sea Security and the Turkish Straits: A Complete Guide

By WPD Editorial Team. This guide separates documented facts from official positions. See Editorial Principles: How WorldPoliticsDaily Separates Fact from Position for how we do that.

Why It Matters

The Black Sea is one of the world's busiest regional trade and energy corridors, and almost everything entering or leaving it by ship passes through the Turkish Straits. The Russia-Ukraine war has turned this semi-enclosed sea into an active zone of naval conflict, grain diplomacy and mine risk, with the legal rules of a 1936 treaty sitting at the centre of the debate. Understanding who controls what, and under which legal rules, explains many of the choices made by Ankara, Moscow, Kyiv and NATO.

Background: Geography, Law and Timeline

The Turkish Straits in brief

The Turkish Straits consist of the Bosphorus (about 31 km or 19 miles long, narrowing to roughly 700 m or 2,300 ft), the Sea of Marmara, and the Dardanelles (about 61 km or 38 miles long). Istanbul, a city of many millions, sits astride the Bosphorus, which is why navigation there is both a legal question and a public-safety question. Tens of thousands of vessels pass each year, including tankers, bulk carriers carrying grain, and container ships.

The Black Sea has six coastal (riparian) states: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia. Because the only sea exit runs through Turkish territory, Türkiye holds a unique position: it is a NATO member, a Black Sea state, and the guardian of the passage that other navies must use to enter or leave.

From Lausanne to Montreux

The 1923 Lausanne Straits Convention demilitarised the Straits and placed them under an international commission. Türkiye argued that this left its largest city exposed. At a conference in Montreux, Switzerland, the parties signed a new convention on 20 July 1936, and it entered into force on 9 November 1936. It restored Turkish sovereignty over the Straits, including the right to remilitarise them, while preserving the principle of free commercial passage. The signatories included Türkiye, the United Kingdom, France, the Soviet Union, Greece, Bulgaria, Romania, Yugoslavia and Japan. Russia is treated as the successor to the Soviet Union's rights. For a full treaty walk-through, read What Is the Montreux Convention and How Does It Govern the Turkish Straits?.

What Montreux actually says

The treaty draws a sharp line between civilian and military shipping.

Category	Peacetime rule	Wartime rule
Merchant ships	Free passage by day and night, subject to Turkish health, safety and navigation rules	If Türkiye is neutral, passage is free for ships not belonging to a state at war with Türkiye... but belligerents' ships follow Articles 2-6 conditions; Türkiye retains wide discretion if it is itself at war or threatened
Warships of Black Sea states	Passage allowed with advance notice; special rules for capital ships and submarines (submarines mainly to return to their home base or go for repair)	Belligerent warships barred under Article 19, except returning to their base
Warships of non-Black Sea states	Notice of 15 days; individual ships generally limited to 15,000 tons; combined tonnage in the Black Sea capped (30,000 tons, rising to a higher ceiling under set conditions); stay limited to 21 days; no aircraft carriers or submarines	Barred if belonging to a belligerent, per Article 19

Two provisions matter most today:

• Article 19: if Türkiye is not at war, warships of belligerent states may not pass the Straits. Ships returning to a base on their own sea are the exception.
• Article 21: if Türkiye considers itself threatened with imminent danger of war, it may decide on its own whether to allow warship passage.

The treaty also gives Türkiye the task of applying and supervising these rules, which is why its legal interpretation carries so much weight.

Key dates

• 1936-07-20: Montreux Convention signed.
• 1952: Türkiye joins NATO.
• 2014: Russia annexes Crimea. The UN General Assembly (Resolution 68/262) affirmed Ukraine's territorial integrity, and Türkiye does not recognise the annexation.
• 2022-02-24: Russia launches its full-scale invasion of Ukraine.
• 2022-02-28: Türkiye announces it will apply Article 19.
• 2022-03-29: Russian and Ukrainian delegations meet in Istanbul for talks.
• 2022-07-22: Black Sea Grain Initiative signed in Istanbul.
• 2023-07-17: The grain deal lapses when Russia declines to extend it.
• 2024-01-11: Türkiye, Romania and Bulgaria sign a mine countermeasures agreement in Istanbul.

The Naval Balance

Before 2022, Russia's Black Sea Fleet, based at Sevastopol in Crimea and at Novorossiysk, was by far the strongest naval force in the sea. Ukraine's conventional navy was small. NATO's Black Sea presence rests mainly on three coastal members: Türkiye, which has one of the alliance's largest navies, plus Romania and Bulgaria, whose fleets are smaller. Other NATO navies can enter only within the Montreux limits.

The war has changed the picture without producing a clear naval victor. Russia lost the cruiser Moskva in April 2022. Ukraine said it hit the ship with missiles, while Russia said a fire and ammunition explosion caused the loss. Ukrainian missiles, uncrewed surface vessels and aerial drones have since hit other Russian ships and shore facilities, and Russian vessels have been reported to shift away from Crimea's main base. Russia, in turn, has struck Ukrainian ports such as Odesa and has threatened shipping bound for Ukrainian harbours. In July 2023 the Russian Defence Ministry said it would treat vessels heading to Ukrainian ports as potential carriers of military cargo.

The practical result is a contested sea in which neither side fully controls commercial lanes. Naval power matters less for classic fleet battles than for missiles, drones, mines and the ability to threaten ports and ships.

Mines, Shipping Risk and Energy

Sea mines are a hazard for civilian ships and coastal states. Drifting mines have been found and neutralised near the Romanian, Bulgarian and Turkish coasts since 2022. Insurers have raised war-risk premiums, and electronic interference such as GPS jamming adds navigational risk. Turkish authorities, who manage traffic through the Straits, have urged ships to follow guidance and report suspicious objects.

In January 2024 Türkiye, Romania and Bulgaria agreed to form the Mine Countermeasures Black Sea task group, with ships and command rotating among the three. The aim is to clear drifting mines and secure commercial routes in the western Black Sea. Because the three states are all NATO members and all Black Sea coastal states, the initiative sits at the junction of regional and alliance security.

Energy also crosses this sea. The TurkStream gas pipeline runs beneath the Black Sea from Russia to Türkiye, and oil from Black Sea ports travels through the Straits by tanker. That is why accidents or closures in the Straits would have effects far beyond the region.

Grain Shipping and the Black Sea Grain Initiative

Ukraine is a major exporter of wheat, maize and sunflower oil, and Russia is a leading wheat and fertiliser exporter. After the invasion, Ukrainian ports were blockaded and food prices spiked. The Black Sea Grain Initiative, brokered by Türkiye and the UN and signed in Istanbul on 22 July 2022, set up a safe corridor for grain from Ukrainian ports. A Joint Coordination Centre in Istanbul, staffed by Turkish, Ukrainian, Russian and UN officials, coordinated inspections. A parallel memorandum between Russia and the UN dealt with Russian food and fertiliser exports.

Russia declined to extend the arrangement in July 2023, saying that the part of the package concerning its own exports had not been delivered. Ukraine, the UN and Western governments said the Initiative was working and urged its renewal. Ukraine later opened its own temporary corridor along its coast. The full mechanics, volumes and disputes are explained in How Did the Black Sea Grain Initiative Work and What Was Türkiye's Role?.

Key Players and Their Positions

Russia. Moscow says Montreux must be applied as written and accuses NATO states of militarising the Black Sea. It considers Black Sea access vital to its navy, to Crimea and to its commodity exports. It ended its participation in the grain deal, citing unfulfilled commitments on its own exports. Russian officials have criticised Western sanctions as an obstacle to agricultural trade.

Ukraine. Kyiv calls on Türkiye to keep Russian warships out of the Black Sea and has asked allies for stronger maritime security. It wants safe commercial corridors, mine clearance and, ultimately, the return of Crimea. It has also argued that a Black Sea left to Russian dominance threatens the whole region.

Türkiye. Ankara is a NATO ally, a Ukraine partner and a trading partner of Russia, and it presents itself as a custodian of Montreux and a mediator. See the dedicated section below.

Romania and Bulgaria. Both are NATO and EU members and the alliance's western Black Sea flank. Romania in particular hosts allied forces and has been vocal about the threat of drifting mines and the need for a stronger allied posture.

Georgia. A Black Sea state and NATO partner whose territory is partly outside government control. Its ports, such as Poti and Batumi, are part of trade routes between Europe and the Caucasus and Central Asia.

NATO. The alliance describes the Black Sea as strategically important, has increased air and maritime surveillance on its eastern flank and supports Ukraine. Its warships' access is shaped by Montreux, so NATO can't simply surge naval forces into the sea.

The EU and the UN. The EU has backed Ukraine's alternative export routes (often called solidarity lanes) and sanctions on Russia, while the UN played a central role in the grain deal and calls for free navigation.

🇹🇷 Official Policy · Primary Turkish Sources

Türkiye's Position

This section summarises Ankara's stated policy, as set out by Turkish government sources. It is labelled separately from the analysis above. Statements are attributed rather than endorsed by WorldPoliticsDaily.

• Montreux is a balanced regime that Türkiye applies impartially. According to the Turkish Foreign Ministry, the 1936 Convention protects both Turkish security and freedom of commercial navigation, and Türkiye implements it as the Straits' sovereign. The legal basis is the treaty text itself, including its provisions on Turkish sovereignty and the Article 19 and 21 powers. Source type: Turkish Foreign Ministry statements on the Straits regime and the treaty text.
• Article 19 applies to everyone. On 27-28 February 2022 Foreign Minister Mevlüt Çavuşoğlu announced that Türkiye would apply Article 19 and warned that the rule covers the warships of all states, whether or not they border the Black Sea, with the exception for returns to home base. Ankara has said this also applies to ships that Western countries wish to send to Ukraine. Source type: Foreign Ministry announcements and ministerial press remarks, February-March 2022.
• Territorial integrity of Ukraine, and dialogue with Russia. Ankara condemned the invasion as unacceptable, voted in favour of the UN General Assembly resolution of 2 March 2022 on Ukraine, and does not recognise the annexation of Crimea. It has not joined Western sanctions on Russia, and Turkish officials argue that keeping open channels to both sides allows Türkiye to broker practical results. Source type: Presidency of the Republic and Foreign Ministry statements; Türkiye's vote record at the UN.
• Mediation as policy. Türkiye hosted the Lavrov-Kuleba meeting in Antalya on 10 March 2022, the Russia-Ukraine delegation talks in Istanbul on 29 March 2022, and the signing of the Grain Initiative on 22 July 2022. President Recep Tayyip Erdoğan has repeatedly called for a ceasefire and a negotiated settlement. Source type: Presidency and Foreign Ministry statements; the Istanbul grain documents.
• Regional ownership of Black Sea security. Ankara has said it wants the Black Sea to remain a sea of peace and cooperation, and it favours mechanisms among coastal states, such as the Black Sea Economic Cooperation organisation, the BLACKSEAFOR naval group and Operation Black Sea Harmony, which it initiated. It presents the 2024 mine countermeasures group as an example of coastal states taking responsibility. Source type: Turkish Foreign Ministry and Ministry of National Defence announcements.

Ankara also says that planned infrastructure such as the Istanbul Canal project would not alter its commitments under Montreux. This was disputed domestically. In April 2021 a group of retired admirals published a statement defending the Convention, which became a political controversy. The government has said that Montreux is not up for renegotiation.

Source Comparison: How the Story Is Framed

Different sources describe the same events in different ways. The table below summarises typical framings; check each source's own statements for exact wording.

Topic	Western and NATO-aligned coverage	Russian official framing	Ukrainian official framing	Turkish official framing
Closure of the Straits	Often says Türkiye 'closed' the Straits to Russian warships	Stresses the exemption for ships returning to base and calls for strict Montreux compliance	Asks for the exemption to be narrowed and Russian ships blocked	Says it applied Article 19 to all belligerents and did not 'close' the Straits to commerce
Grain deal	Credits Türkiye and the UN; blames Russia for ending it	Says its own export commitments were not met	Calls the corridor vital and blames Russian obstruction	Calls it a major diplomatic success and urges its return
NATO in the Black Sea	Treats it as deterrence and support for allies	Treats it as escalation	Seeks stronger allied presence	Prefers coastal-state frameworks and de-escalation, while remaining a NATO ally
Türkiye's role	Mixed: mediator or hedger, depending on outlet	Partner whose neutrality is valued but sometimes criticised	Partner that provides arms and diplomatic support; critics want more pressure	Principled, balanced mediator

A common simplification is that Türkiye 'shut the Straits to Russia'. In treaty terms, Article 19 restricts warships of belligerents, while merchant traffic continues and returning ships are exempt. Claims of this kind are examined in our Fact Check: Claims About Türkiye in International Media category. For a parallel maritime debate in another sea, see Eastern Mediterranean Maritime Disputes Explained: Rights, Maps and Positions.

What to Watch Next

• Treaty stability. No party is currently seeking a formal revision. Disagreements concern interpretation and application, such as what counts as 'returning to base' and how to classify ship types.
• Ceasefire scenarios. After a ceasefire, Article 19 could cease to apply, which would let non-Black Sea navies transit again within Montreux limits. This is one reason why Russia, Ukraine and NATO states all follow Ankara's legal reading closely.
• Mine clearance and insurance costs. Whether the Turkish-Romanian-Bulgarian task group becomes a lasting mechanism will affect commercial confidence.
• Corridors. Ukraine's ability to export by sea, and Russia's ability to export without disruption, will remain tied to the military situation.
• Energy flows. Shipping and pipeline routes through and under the Black Sea remain exposed to the risk of attack or accident.

Glossary: Key Terms

• Riparian state: a state with a coastline on a given sea. Here, Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia.
• Capital ship: a large warship. Montreux restricts the passage of ships above a set tonnage, and generally only Black Sea states may send the largest.
• Article 19: the Montreux provision that bars warships of belligerent states during a war in which Türkiye is neutral, with a return-to-base exception.
• Article 21: the provision allowing Türkiye to decide on warship passage if it faces an imminent threat of war.
• Mine countermeasures (MCM): operations to find, identify and neutralise sea mines.
• Joint Coordination Centre: the Istanbul body that monitored and inspected ships under the Black Sea Grain Initiative.
• PKK: a group Türkiye, the US and the EU list as a terrorist organisation. It is unrelated to the Black Sea but features in other Turkish security debates.

Perspective Note

WorldPoliticsDaily presents global affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources. Facts, chronology and other parties' positions are set out separately and attributed. If you notice an error, please tell us. You can learn more about our approach in Editorial Principles: How WorldPoliticsDaily Separates Fact from Position.

Cross-Publication Dossiers & Sister Desk Perspectives

For complementary primary-source analysis across our specialist editorial network, consult:

• 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.
• Index of Nations: The Montreux Convention and Black Sea Security: How Türkiye Applies the Turkish Straits Regime — Montreux Convention Turkish Straits explained: merchant freedom, warship limits, Article 19 in the Ukraine war, and why Türkiye can't close them at will.
• Archive of Nations: The 1936 Montreux Convention, the Turkish Straits and Black Sea Security in the Russia–Ukraine War — How the 1936 Montreux Convention governs the Turkish Straits in the Russia–Ukraine war: Article 19, warship limits, Istanbul talks and Türkiye's legal powers.