Signed on 20 July 1936 at the Montreux Palace in Switzerland,[4] it went into effect on 9 November 1936, addressing the long running Straits Question over who should control the strategically vital link between the Black and Mediterranean seas.

In peacetime, military vessels are limited in number, tonnage and weaponry, with specific provisions governing their mode of entry and duration of stay.

[6][7][note 1] In wartime, if Turkey is not involved in the conflict, warships of the nations at war may not pass through the Straits, except when returning to their base.

[9] While it was designed for a particular geopolitical context, and remains unchanged since its adoption, the Montreux Convention has endured as a "solid example of a rules-based international order", since most of its terms are still followed.

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.

[12] In April 1935, the Turkish government dispatched a lengthy diplomatic note to the signatories of the Treaty of Lausanne proposing a conference to agree a new regime for the Straits and requested that the League of Nations authorise the reconstruction of the Dardanelles forts.

The Abyssinia Crisis of 1934–1935, 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".

The key weaknesses of the present regime were that the machinery for collective guarantees were too slow and ineffective, and there was no contingency for a general threat of war and no provision for Turkey to defend itself.

The response to the note was generally favourable; Australia, Bulgaria, France, Germany, Greece, Japan, Romania, the Soviet Union, Turkey, the United Kingdom and Yugoslavia attended negotiations at Montreux, Switzerland, which began on 22 June 1936.

Two major powers were notably absent: Italy, whose aggressively expansionist policies had prompted the conference, refused to attend, and the increasingly isolationist United States declined even to send an observer.

[14] Turkey, the United Kingdom and the Soviet Union each put forward their own set of proposals, each aimed chiefly at protecting the proponent's own interests.

The British, supported by France, sought to exclude the Soviet fleet from the Mediterranean Sea, where it might threaten the vital shipping lanes to India, Egypt and the Far East.

[17] Britain's willingness to make concessions has been attributed to a desire to avoid Turkey being driven to ally itself with or to fall under the influence of Adolf Hitler or Benito Mussolini.

[18][19] 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.

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".

This feature was to have significant repercussions during World War II; the Montreux regime prevented the Axis powers from sending naval forces through the Straits to attack the Soviet Union.

[citation needed] The Axis powers, thereby, were severely limited in naval capability for their Black Sea campaigns, relying principally on small vessels transported overland by rail and canal networks.

[42] Soviet pressure expanded into a full demand to revise the Montreux Convention, which led to the 1946 Turkish Straits crisis and Turkey abandoning its policy of neutrality.

The Turkish government rejected 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.

[45] The US thinktank Stratfor has suggested that those stipulations place Turkey's relationship to the US and its obligations as a NATO member in conflict with Russia and the regulations of the Montreux Convention.

[46] The Convention annulled the terms of the earlier Lausanne Treaty on the Straits, including the demilitarisation of the Greek islands of Lemnos and Samothrace.

Turkey recognised Greece's right to militarise them via a letter sent to the Greek Prime Minister on 6 May 1936 by the Turkish Ambassador in Athens, Ruşen Eşref.

[52] After initial reluctance, attributed to the country's close ties with both Russia and Ukraine,[52] Turkish Foreign Minister Mevlüt Çavuşoğlu announced on 27 February that his government would legally recognise the Russian invasion as a "war", which provides grounds for implementing the convention with respect to military vessels.

Since this was becoming more difficult to justify, one analysis in May 2022 suggested that the Russians may have found a work-around to the problem, potentially using the country's internal waterways to permit transit to vessels up to the size of the Kilo-class boats between the Black Sea and the Baltic.