Montreux Convention Regarding the Regime of the Straits

Montreux Convention Regarding the Regime of the Straits
Type Multilateral treaty
Signed 20 July 1936 (1936-07-20)
Location Montreux, Switzerland
Effective 9 November 1936 (1936-11-09)

The Montreux Convention Regarding the Regime of the Straits is a 1936 agreement that gives Turkey control over the Bosporus and Dardanelles Straits and regulates the transit of naval warships. The Convention guarantees the free passage of civilian vessels in peacetime, and restricts the passage of naval ships not belonging to Black Sea states. The terms of the Convention have been a source of controversy over the years, most notably about the Soviet Union's military access to the Mediterranean Sea.

Signed on 20 July 1936 at the Montreux Palace in Switzerland,[1] the Convention permitted Turkey to remilitarise the Straits. It went into effect on 9 November 1936 and was registered in the League of Nations Treaty Series on 11 December 1936.[2] It remains in force.

The 21st century Kanal Istanbul (Istanbul Canal) project, currently under construction, may circumvent the Montreux Convention and allow greater Turkish autonomy with respect to the passage of military ships (which are limited in number, tonnage, and weaponry) from the Black Sea to the Sea of Marmara. The Kanal project involves building a 45 km (28 mi) long artificial waterway through Thrace, connecting the Sea of Marmara with the Black Sea.[3] While this route will run nearly parallel to the Bosporus, ships transiting it are arguably not subject to the terms of the Montreux Convention.[4] Currently shipping traffic through the Dardanelles is heavily congested, with long wait times to pass through the Bosporus. The Kanal project‘s primary purpose is to clear up shipping traffic and boost revenue by providing an alternate maritime route. However, the Kanal’s potential ability to end nearly a century of limitations imposed by the Montreux regime was never overlooked by both commentators and politicians, and in January 2018, then Turkish Prime Minister and former Transport Minister Binali Yıldırım announced that the Kanal would in fact not be subject to the Montreux Convention.[5] This announcement was received negatively by the Russian media and government and many have disputed the Turkish government‘s interpretation of the convention‘s original terms.[6][7]


The convention was one of a series of agreements in the 19th and 20th centuries that sought to address the long-running Straits Question of who should control the strategically vital link between the Black Sea and Mediterranean Sea. In 1923, the Treaty of Lausanne had demilitarised the Dardanelles and opened the Straits to unrestricted civilian and military traffic, under the supervision of the International Straits Commission of the League of Nations.

By the late 1930s, the strategic situation in the Mediterranean had altered with the rise of Fascist Italy, which controlled the Greek-inhabited Dodecanese islands off the west coast of Turkey and had constructed fortifications on Rhodes, Leros and Kos. The Turks feared that Italy would seek to exploit access to the Straits to expand its power into Anatolia and the Black Sea region. There were also fears of Bulgarian rearmament.[8] Although Turkey was not permitted to refortify the Straits, it nonetheless did so secretly.[9]

In April 1935, the Turkish government dispatched a lengthy diplomatic note to the signatories of the Treaty of Lausanne proposing a conference on the agreement of a new regime for the Straits and requested that the League of Nations authorise the reconstruction of the Dardanelles forts. In the note, Turkish foreign minister Tevfik Rüştü Aras explained that the international situation had changed greatly since 1923. At that time, Europe had been moving towards disarmament and an international guarantee to defend the Straits. The Abyssinia Crisis of 1934–35, the denunciation by Germany of the Treaty of Versailles and international moves towards rearmament meant that "the only guarantee intended to guard against the total insecurity of the Straits has just disappeared in its turn." Indeed, Aras said, "the Powers most closely concerned are proclaiming the existence of a threat of general conflagration." The key weaknesses of the present regime were that the machinery for collective guarantees were too slow and ineffective, there was no contingency for a general threat of war and no provision for Turkey to defend itself. Turkey was therefore prepared

to enter into negotiations with a view to arriving in the near future at the conclusion of agreements for regulations of the regime of the Straits under the conditions of security which are indispensable for the inviolability of Turkey's territory, in most liberal spirit, for the constant development of commercial navigation between the Mediterranean and the Black Sea.

The response to the note was generally favourable, and Australia, Bulgaria, France, Germany, Greece, Japan, Romania, the Soviet Union, Turkey, the United Kingdom and Yugoslavia agreed to attend negotiations at Montreux in Switzerland, which began on 22 June 1936. Two major powers were not represented: Italy, whose aggressively expansionist policies had prompted the conference in the first place, refused to attend and the United States declined even to send an observer.[10]

Turkey, the UK and the Soviet Union each put forward their own set of proposals, aimed chiefly at protecting their own interests. The British favoured the continuation of a relatively restrictive approach, while the Turks sought a more liberal regime that reasserted their own control over the Straits and the Soviets proposed a regime that would guarantee absolute freedom of passage. The British, supported by France, sought to exclude the Soviet fleet from the Mediterranean Sea, where it might have threatened the vital shipping lanes to India, Egypt and the Far East.[11] In the end, the British conceded some of their requests while the Soviets succeeded in ensuring that the Black Sea countries – including the USSR – were given some exemptions from the military restrictions imposed on non-Black Sea nations. The agreement was ratified by all of the conference attendees with the exception of Germany, which had not been a signatory to the Treaty of Lausanne, and with reservations by Japan,[12] and came into force on 9 November 1936.[10]

Britain's willingness to make concessions has been attributed to a desire to avoid Turkey being driven to ally itself with, or fall under the influence of, Adolf Hitler or Benito Mussolini.[13][14] It was thus the first in a series of steps by Britain and France to ensure that Turkey would either remain neutral or tilt towards the Western Allies in the event of any future conflict with the Axis.[10]


As mentioned in the preamble, the Convention annulled the previous Lausanne Treaty on the Straits, which stated the demilitarization of the Greek islands of Lemnos and Samothrace along with the demilitarization of the Dardanelles, the Sea of Marmara and the Bosporus, and the Turkish islands of İmroz, Bozcaada and Tavşan.

The Convention consists of 29 Articles, four annexes and one protocol. Articles 2–7 consider the passage of merchant ships. Articles 8–22 consider the passage of war vessels. The key principle of freedom of passage and navigation is stated in articles 1 and 2. Article 1 provides, "The High Contracting Parties recognise and affirm the principle of freedom of passage and navigation by sea in the Straits". Article 2 states, "In time of peace, merchant vessels shall enjoy complete freedom of passage and navigation in the Straits, by day and by night, under any flag with any kind of cargo."

The International Straits Commission was abolished, authorising the full resumption of Turkish military control over the Straits and the refortification of the Dardanelles. Turkey was authorised to close the Straits to all foreign warships in wartime or when it was threatened by aggression. Also, it was authorised to refuse transit from merchant ships belonging to countries at war with Turkey.

A number of highly-specific restrictions were imposed on what type of warships are allowed passage. Non-Black-Sea powers willing to send a vessel must notify Turkey 8 days prior of their sought passing. Also, no more than nine foreign warships, with a total aggregate tonnage of 15,000 tons, may pass at any one time. Furthermore, no single ship heavier than 10,000 tonnes can pass.[15] An aggregate tonnage of all non-Black Sea warships in the Black Sea must be no more than 30,000 tons (or 45,000 tons under special conditions), and they are permitted to stay in the Black Sea for no longer than twenty-one days. Only Black Sea states may transit capital ships of any tonnage, escorted by no more than two destroyers.

Under Article 12, Black Sea states are also allowed to send submarines through the Straits, with prior notice, as long as the vessels have been constructed, purchased or sent for repair outside the Black Sea. The less restrictive rules applicable to Black Sea states were agreed as, effectively, a concession to the Soviet Union, the only Black Sea state other than Turkey with any significant number of capital ships or submarines.[14][16] The passage of civil aircraft between the Mediterranean and Black Seas is permitted but only along routes authorised by the Turkish government.[17]

In operation

The terms of the Convention were largely a reflection of the international situation in the mid-1930s. They largely served Turkish and Soviet interests, enabling Turkey to regain military control of the Straits and assuring Soviet dominance of the Black Sea.[17] Although the Convention restricted the Soviets' ability to send naval forces into the Mediterranean Sea, thereby satisfying British concerns about Soviet intrusion into what was considered a British sphere of influence, it also ensured that outside powers could not exploit the Straits to threaten the Soviet Union. That was to have significant repercussions during World War II when the Montreux regime prevented the Axis powers from sending naval forces through the Straits to attack the Soviet Union.[citation needed] The Axis powers were thus severely limited in naval capability in their Black Sea campaigns, relying principally on small vessels that had been transported overland by rail and canal networks.

Auxiliary vessels and armed merchant ships occupied a grey area, however, and the transit of such vessels through the straits led to friction between the Allies and Turkey. Repeated protests from Moscow and London led to the Turkish government banning the movements of "suspicious" Axis ships with effect from June 1944 after a number of German auxiliary ships had been permitted to transit the Straits.[18][19]

Aircraft carriers

Although the Montreux Convention is cited by the Turkish government as prohibiting aircraft carriers from transiting the straits,[20] the treaty actually contains no explicit prohibition on aircraft carriers. However, modern aircraft carriers are heavier than the 15,000 ton limit imposed on warships, making it impossible for non-Black Sea powers to transit modern aircraft carriers through the Straits.

Under Article 11, Black Sea states are permitted to transit capital ships of any tonnage through the straits, but Annex II specifically excludes aircraft carriers from the definition of capital ship. In 1936, it was common for battleships to carry observation aircraft. Therefore, aircraft carriers were defined as ships that were "designed or adapted primarily for the purpose of carrying and operating aircraft at sea." The inclusion of aircraft on any other ship does not classify it as an aircraft carrier.[21]

The Soviet Union designated its Kiev-class and Kuznetsov-class ships as "aircraft-carrying cruisers" because these ships were armed with P-500 and P-700 cruise missiles, which also form the main armament of the Slava-class cruiser and the Kirov-class battlecruiser. The result was that the Soviet Navy could send its aircraft-carrying cruisers through the Straits in compliance with the Convention, but at the same time the Convention denied access to NATO aircraft carriers, which exceeded the 15,000 ton limit.[22][23][24][25]

Turkey chose to accept the designation of the Soviet aircraft carrying cruisers as aircraft cruisers, as any revision of the Convention could leave Turkey with less control over the Turkish Straits, and the UN Convention on the Law of the Sea had already established more liberal passage through other straits. By allowing the Soviet aircraft carrying cruisers to transit the Straits, Turkey could leave the more restrictive Montreux Convention in place.[25]


Soviet Union

The Convention remains in force, but not without dispute. It was repeatedly challenged by the Soviet Union during World War II and the Cold War. As early as 1939, Joseph Stalin sought to reopen the Straits Question and proposed joint Turkish and Soviet control of the Straits, complaining that "a small state [i.e. Turkey] supported by Great Britain held a great state by the throat and gave it no outlet".[26] After the Molotov–Ribbentrop Pact was signed by the Soviet Union and Nazi Germany, the Soviet Foreign Minister Vyacheslav Molotov informed his German counterparts that the Soviet Union wished to take military control of the Straits and establish its own military base there.[27] The Soviets returned to the issue in 1945 and 1946, demanding a revision of the Montreux Convention at a conference excluding most of the Montreux signatories, a permanent Soviet military presence and joint control of the Straits. That was firmly rejected by Turkey, despite an ongoing Soviet "strategy of tension". For several years after World War II, the Soviets exploited the restriction on the number of foreign warships by ensuring that one of theirs was always in the Straits, thus effectively blocking any state other than Turkey from sending warships through the Straits.[28] Soviet pressure expanded into full demands to revise the Montreux Convention, which led to the Turkish Straits crisis of 1946, which led to Turkey abandoning its policy of neutrality. In 1947, it became the recipient of US military and economic assistance under the Truman Doctrine of containment and joined the NATO alliance, along with Greece, in 1952.[29]

United States

The passage of US warships through the Straits also raised controversy, as the convention forbids the transit of non-Black Sea nations' warships with guns of a calibre larger than eight inches (203 mm). In the 1960s, the US sent warships carrying 420 mm calibre ASROC missiles through the Straits, prompting Soviet protests. The Turkish government rejected the Soviet complaints, pointing out that guided missiles were not guns and that since such weapons had not existed at the time of the Convention, they were not restricted.[30]

According to news editor Jason Ditz, the Montreux Convention is an obstacle to US Naval buildup in the Black Sea because of its stipulations regulating warship traffic by nations not sharing Black Sea coastline.[31] The US thinktank Stratfor has written that these stipulations place Turkey's relationship to the US and its obligations as a NATO alliance member in conflict with Russia and the regulations of the Montreux Convention.[32]

Militarisation of the Greek islands

The Convention annulled the previous Lausanne Treaty on the Straits, including the demilitarization of the Greek islands of Lemnos and Samothrace. Greece’s right to militarise them was recognized by Turkey, in accordance with the letter sent to the Greek Prime Minister on 6 May 1936 by the Turkish Ambassador in Athens at the time, Ruşen Eşref, upon instructions from his Government. The Turkish government reiterated this position when the then Turkish Minister for Foreign Affairs, Rüştu Aras, in his address to the Turkish National Assembly on the occasion of the ratification of the Montreux Treaty, unreservedly recognized Greece’s legal right to deploy troops on Lemnos and Samothrace, with the following statement: "The provisions pertaining to the islands of Limnos and Samothrace, which belong to our neighbor and friendly country Greece and were demilitarized in application of the 1923 Lausanne Treaty, were also abolished by the new Montreux Treaty, which gives us great pleasure".[33]

After the relationship between the countries deteriorated over the next decades, Turkey denied that the treaty affected the Greek islands, seeking to bring back into force the relevant part of the Lausanne Treaty on the Straits.[34][35]

1994 reforms

The United Nations Convention on the Law of the Sea (UNCLOS), which entered into force in November 1994, has prompted calls for the Montreux Convention to be revised and adapted to make it compatible with UNCLOS's regime governing straits used for international navigation. However, Turkey's longstanding refusal to sign UNCLOS has meant that Montreux remains in force without further amendments.[36]

The safety of vessels passing through the Bosporus has become a major concern in recent years as the volume of traffic has increased greatly since the Convention was signed: from 4,500 in 1934 to 49,304 by 1998. As well as obvious environmental concerns, the Straits bisect the city of Istanbul, with over 14 million people living on its shores and so maritime incidents in the Straits pose a considerable risk to public safety. The Convention does not, however, make any provision for the regulation of shipping for the purposes of safety and environmental protection. In January 1994, the Turkish government adopted new "Maritime Traffic Regulations for the Turkish Straits and the Marmara Region". That introduced a new regulatory regime "to ensure the safety of navigation, life and property and to protect the environment in the region" but without violating the Montreux principle of free passage. The new regulations provoked some controversy when Russia, Greece, Cyprus, Romania, Ukraine and Bulgaria raised objections. However, they were approved by the International Maritime Organization on the grounds that they were not intended to prejudice "the rights of any ship using the Straits under international law". The regulations were revised in November 1998 to address Russian concerns.[37]


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