Regarding the Montreaux Convention, this from Wikipedia:
The Convention remains in force today, with amendments, though not without dispute. It was repeatedly challenged by the Soviet Union during World War II and the Cold War. As early as 1939, 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.”[12] 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 USSR wished to take military control of the Straits and establish its own military base there.[13] 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. This 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 nation other than Turkey from sending warships through the Straits.[14] Soviet pressure eventually resulted in 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 NATO, along with Greece, in 1952.[15]
The Soviet Union and its successor, the Russian Federation, have repeatedly sought to evade the ban on aircraft carriers passing through the Straits by designating large aircraft-carrying warships as “heavy aircraft carrying cruisers”, although Western nations regard such ships as aircraft carriers. In 1976, the USSR sent the aircraft carrier Kiev through the Straits. The episode was repeated in 1991 when the Russian aircraft carrier Admiral Kuznetsov transited the straits.[8]
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 305 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 such weapons had not even existed at the time of the Convention’s signature so were not restricted by the Convention.[16]
In April 1982, the Convention was amended to allow Turkey to close the Straits at its discretion in peacetime as well as during wartime.[17]
The United Nations Convention on the Law of the Sea (LOS Convention), which entered into force in November 1994, has prompted calls for the Montreux Convention to be revised and adapted to make it compatible with the LOS Convention’s regime governing straits used for international navigation. However, Turkey’s long-standing refusal to sign the LOS Convention has meant that Montreux remains in force without further amendments
