Montreux Convention Regarding the Regime of the Straits
The Montreux Convention of 1936 is an international agreement that establishes the legal framework governing passage through the Bosporus and Dardanelles straits, two strategically significant waterways linking the Black Sea to the Mediterranean. Signed at the Montreux Palace in Switzerland on 20 July 1936 and entering into force on 9 November 1936, the Convention remains central to regional security, naval diplomacy, and commercial navigation. Although drafted for the interwar geopolitical environment, its provisions continue to shape maritime operations in the twenty-first century.
Historical background
Throughout the nineteenth and early twentieth centuries, the “Straits Question” dominated diplomatic discussions concerning balance of power in southeastern Europe and the eastern Mediterranean. The Straits provide the only maritime outlet for Black Sea states and therefore became a focal point for international rivalry, particularly among Russia, Britain, and the Ottoman Empire. The post-First World War settlement attempted to stabilise the situation through the 1923 Treaty of Lausanne, which demilitarised the Dardanelles and placed control of the Straits under the supervision of the International Straits Commission operating within the League of Nations framework. Lausanne granted broad rights of passage to both civilian and military shipping.
By the mid-1930s, however, the strategic environment had shifted sharply. Fascist Italy’s assertive expansionism, reflected in its occupation of the Dodecanese islands and construction of fortified bases in the Aegean, raised concerns in Ankara that Italian naval forces might exploit unrestricted access to threaten Turkish security or project power into the Black Sea. At the same time, regional rearmament, including Bulgarian military developments, undercut the assumptions underpinning Lausanne’s demilitarised regime.
In April 1935, the Turkish government formally requested the signatories of the Lausanne Treaty to reconvene and revise the Straits regime. Turkey argued that collective security mechanisms had failed in the face of crises such as the Abyssinia conflict and that Ankara required the right to defend its territory and maritime approaches. The diplomatic note presented by Foreign Minister Tevfik Rüştü Aras emphasised that the international system was drifting towards widespread conflict and that the Straits regime must therefore be adapted to contemporary threats.
Negotiations opened at Montreux on 22 June 1936 with participation from Australia, Bulgaria, France, Germany, Greece, Japan, Romania, the Soviet Union, Turkey, the United Kingdom, and Yugoslavia. Italy refused to attend, while the United States, adopting an isolationist posture, declined to send observers. Each major participant submitted proposals reflecting national strategic priorities. Britain sought continued restrictions designed to limit Soviet naval access to the Mediterranean, a region critical to Imperial communications. Turkey pressed for a liberalised regime restoring sovereignty and defensive capabilities. The Soviet Union advocated broad freedom of passage for Black Sea states.
The final agreement constituted a compromise: Britain abandoned several demands, Turkey recovered the right to fortify the Straits, and the Soviet Union secured exemptions for Black Sea nations from the most stringent tonnage and passage restrictions. Germany did not ratify the agreement, and Japan ratified with reservations. The Convention was registered with the League of Nations Treaty Series in December 1936. Britain’s conciliatory stance has often been interpreted as part of an effort to maintain Turkey’s neutrality or to align Ankara informally with the Western powers in anticipation of future tensions with the Axis powers.
Structure and legal framework of the Convention
The Montreux Convention comprises twenty-nine articles, four annexes, and an additional protocol. It replaced the Lausanne provisions relating to the Straits and abolished the International Straits Commission, restoring full Turkish control and permitting the fortification of the Dardanelles. The Convention maintains a balance between guaranteeing commercial freedom of navigation and addressing legitimate security interests of both Turkey and Black Sea states.
Articles 1 and 2 articulate the key principles. Freedom of passage and navigation through the Straits is recognised as a fundamental right of all merchant vessels during peacetime. Passage is permitted by day and night, under all flags and with any cargo. Merchant shipping of states at war with Turkey may be restricted, reflecting the sovereign right of self-defence.
Articles 8 to 22 regulate the transit of warships and include some of the Convention’s most detailed provisions. The regime distinguishes between Black Sea and non-Black Sea powers. Non-Black Sea navies wishing to send warships through the Straits must provide at least fifteen days’ notice to Turkish authorities, whereas Black Sea states must provide eight days. The Convention imposes strict limits on the number, tonnage, and type of warships permitted to transit at one time. No more than nine foreign warships may pass simultaneously, with a combined tonnage not exceeding 15,000 tons. Individual ships heavier than 10,000 tons may not pass, and all non-Black Sea powers are collectively restricted to a maximum Black Sea presence of 45,000 tons, with any one navy limited to 30,000 tons. Warships of non-Black Sea states may remain in the Black Sea for no longer than twenty-one days. Only Black Sea states may transit capital ships through the Straits.
The Convention grants Turkey significant wartime latitude. If Turkey is neutral during a conflict, warships belonging to belligerents may not pass through the Straits except when returning to their bases. Should Turkey be a belligerent or consider itself threatened by imminent danger of war, it may take any decisions it deems necessary regarding passage, including closure of the Straits. These provisions reflect the unique geostrategic position of Turkey and the desire of signatory states to prevent escalation in such a sensitive maritime corridor.
Significance for international relations and maritime security
The Montreux Convention stands as a prominent example of a rules-based maritime governance regime that has remained largely unchanged for nearly a century. Its endurance highlights the stability afforded by clear legal norms and mutual recognition of the strategic sensitivities associated with the Straits. For Black Sea powers in particular, the Convention provides predictable access to the Mediterranean while limiting the ability of non-regional navies to project power into the Black Sea.
For Turkey, the Convention represents both a restoration of sovereignty and a cornerstone of national security policy. Control over the Straits, combined with the right to regulate military passage, grants Ankara substantial influence over regional naval dynamics. The Convention also reinforces Turkey’s role as a maritime gatekeeper between Europe and Asia, shaping its diplomatic relations with neighbouring states and extra-regional powers.
Although drafted for an earlier geopolitical environment, the Convention continues to guide the movement of civilian shipping and military vessels. Its restrictions on warship tonnage and duration of stay have ongoing relevance in maintaining regional stability, particularly in the context of contemporary tensions involving Black Sea states. Regular references to the Convention in international discourse demonstrate that its principles remain widely respected even by countries, such as the United States, that are not signatories.
