Ukraine Symposium – The Montreux Convention and Turkey’s Impact on Black Sea Operations – Lieber Institute West Point

Weeks into Russia’s military campaign into Ukraine, the role homeported Black Sea maritime forces are playing is well documented. Reuters recently published a story in which the Russian Defense Minister confirmed that Russia struck Ukraine with Kalibr cruise missiles from ships in the Black Sea. The Moscow Times, an ardent anti-Putin paper, also published a report discussing Ukrainian naval forces’ use of mines in and around ports to ward off Russian littoral-based attacks. Al Jazeera is reporting that Ukrainians have placed mines along the shore of the Black Sea outside of Odessa. And just recently, the world watched toppling of  the Moskva, Russia’s flagship vessel in the Black Sea, which the Pentagon confirmed was the result of a successful Ukrainian missile strike.

But a critical feature of this conflict has received little attention, despite the fact that it may become a central tenet of the war: Turkey’s legal authority to control transits through the Turkish Straits that have a direct bearing on maritime operations in the Black Sea. To date, only a handful of articles have analyzed this issue (see, for example, Mark Nevitt’s February 28 post on Just Security, Raul (Pete) Pedrozo’s March 3 post here on Articles of War, and Cornell Overfield’s March 5 post on Lawfare Blog). Each lays out the history and central tenets of the Montreux Convention (formally known as the 1936 Convention Regarding the Regime of the Straits), which governs the transit of commercial and military vessels alike through the Turkish Straits.

Montreux Convention Articles 19, 20, and 21

There are three provisions in the Montreux Convention that set out Turkey’s legal authority to control transits through the Turkish Straits: Articles 19, 20, and 21.

Article 19, which applies “[i]n a time of war” when “Turkey is not a belligerent,” provides that non-belligerent States’ “warships shall enjoy complete freedom of transit and navigation through the Straits” just as they do under peacetime rules, while belligerent States’ “warships shall not … pass through the Straits” unless (1) they are acting under lawful collective defense rights or obligations, or (2) they are forced to make the voyage to return to their home base.

Article 20, which applies when Turkey deems itself a belligerent in the conflict in question, suspends certain peacetime rules and provides that the “passage of warships shall be left entirely to the discretion of the Turkish Government.”

Finally, Article 21 straddles Articles 19 and 20, applying when Turkey “considers itself to be threatened with imminent danger of war.” In such situations, as Overfield states, “peacetime rules on warship navigation are suspended under Article 21,” though “ships separated from their bases by the [S]traits must generally be allowed to transit to return home.”

By the time Nevitt, Pedrozo, and Overfield published their pieces, Turkey had already declared the conflict between Russia and Ukraine a “war” for the purposes of Montreux Convention. As Nevitt notes, this triggers Article 19, meaning that Russian and Ukrainian ships—as warships of a designated “belligerent” State—would only be permitted to transit the Straits to return to their home bases. Resultantly, Moscow ordered several ships of the Black Sea fleet to return to their home ports in the Black Sea.

In early March, Russia attempted to use this justification as a cover story to bring additional ships into the theater. Turkey ferreted out the Kremlin’s plan and objected to those ships transiting the Straits because they were not heading “home.”

It is essential to acknowledge that the Montreux Convention affords wide latitude for Turkey to determine the nature and scope of a conflict unilaterally. This allows Turkey to effectively dictate which of these powers, if any, are triggered based on its own subjective assessment of current events. Thus, the text of Montreux yields significant leverage to the Turkish government, which, in turn, can manifest an outsized operational impact on interested maritime nations. This matters for two interrelated yet independent reasons.

 Implications for Future Attacks against NATO Nations

 First, there is potential that the North Atlantic Treaty (Article 5 in particular) impacts Turkey’s application of the Montreux Convention—yielding significant strategic effects. NATO Member States bordering Ukraine faced the imminent prospect of Russian attacks spilling onto their territory as hostilities commenced in February. Similarly, throughout the conflict, there have been notable examples of Russian military activities spreading to the shores of NATO Member States.

Though Russia ostensibly shifted its focus to Eastern Ukraine in recent days—thus decreasing the threat to NATO Member States—the potential that they resume campaigning near Polish, Romanian, or Slovakian territory remains. Accordingly, Poland has increased its military exercises in recent days in preparation for hostilities, while Slovakia may be seen as giving aid to Ukraine with its recent “donation” of anti-aircraft weaponry to Ukraine—inviting Russian ire.

In its last several official statements, NATO assertively reaffirmed its “iron-clad” commitment to Article 5 and assured that its Member States remain firmly committed to united defense. Should Russian hostility actually spill into the aforementioned territory, Turkey is treaty-bound to at least consider those attacks as attacks on itself. (This is a substantially lesser concern with regard to Hungary, another NATO member that borders Ukraine, as Hungarian Prime Minister Viktor Orban is considered by some to be aiding Russia.)

Article 5 of the North Atlantic Treaty provides that if one “NATO ally is the victim of an armed attack, every other member of the Alliance will consider this act of violence as an armed attack against all members and will take the actions it deems necessary to assist the Ally attacked.”(emphasis added). Following military activity taking place within the territory of a NATO Member State, the organization will “meet to discuss whether they agree that actions on the ground rise to the level of invoking Article 5.”

Importantly, in recent years, NATO affirmed a more expansive view of what constitutes an “armed attack.” In its June 2021 communiqué, NATO stated that it would convene a meeting in the wake of hybrid–or cyber–attacks to consider if the matter rose to the level of an “armed attack”—at least somewhat broadening Article 5’s aperture. If NATO signatories agree that the attack in question rises to such a level, and NATO formally invokes Article 5, Turkey could squarely declare itself a belligerent in the Montreux context, unlocking Article 20.

Should this happen, Article 20 allows Turkey to take whatever action it deems appropriate concerning Straits transit. Article 5 does not require one NATO nation’s actions to be calibrated with those of other States. The text of Article 5 yields that in the wake of an “armed attack,” each allied nation “will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary…to restore and maintain the security of the North Atlantic area.” (emphases added). In other words, post-consensus, a nation retains discretion on what form of support it will provide and the attendant quality and quantity of that support.

This reading is not only supported by the text of the Article itself but has been interpreted as such. According to Edgar Buckley, NATO’s Assistant Secretary General for Defence Planning and Operations from 1999-2003, when Article 5 was debated in 2001 following the September 11 attacks, NATO’s legal advisor issued a memorandum to all Member States instructing that should Article 5 be officially invoked and a consensus reached, it “was [then] up to each Ally to judge for itself what action needed to be taken, although such action should be appropriate to the scale of the attack, the means of each country and the steps necessary to restore peace and security.” So even if some view Turkey’s actions in the Straits as unsuitably escalatory in the wake of an Article 5 invocation, it matters not.

Turkey can arguably go a step further with the collective defense commitment under Article 5. Reading both NATO Article 5 and Montreux Convention provisions together, there is little codified in either agreement to stop Ankara from suggesting that it is “threatened with imminent danger of war” when another NATO Member State is subject to Russian hostilities near its border. Thus, Turkey could theoretically argue that they are obligated to act in anticipatory defense of a NATO ally, triggering Article 21.

This argument may be somewhat textually difficult, however. Moreover, in December, NATO re-asserted that the Alliance would act as a collective body towards Russia—preventing a piecemeal approach to the application of the treaty. That being said, there is nothing limiting Turkish discretion in the applicable agreements or historical precedent. This is to simply say that Turkey could attempt to support an invocation of Article 21—which is largely unchecked, as mentioned—with an anticipatory defense argument derived from the NATO Treaty. That is not to say that Turkey would be correct or incorrect in this interpretation, but rather simply putting forward how Turkey could interpret the world it faces and its treaty obligations.

A Threat to Turkey

The expansion of both potential and actual hostilities in Ukraine more broadly, even absent an attack on a NATO nation and an invocation of NATO Article 5, lays the groundwork for Turkey to “[consider] itself to be threatened with imminent danger of war” and invoke Montreux Article 21. Russian mines washing ashore in Turkish territory certainly adds credence to a potential Article 21 invocation.

To date, Turkey has only given murky comments about its position vis-à-vis “imminent danger”—typifying the outsized discretion it retains under the Montreux Convention. On February 28, Turkish Foreign Minister Mevlüt Çavuşoğlu “warned all riparian and non-riparian countries not to let warships go through the Straits.” Pedrozo argued that Turkey went beyond the confines of Article 19 and de facto bled into Article 21. We agree with his assessment. So far, Turkey has only affirmatively invoked Article 19 (i.e., there is a war, and the belligerents, Russia and Ukraine, must not transit warships through Straits but for returning to homeport). But the Foreign Minister’s declaration of a transit prohibition for all States, though likely de-escalatory, necessitates invocation of either Article 20 or 21 of the Convention. But because Turkey has not yet overtly declared that it is in immediate danger, and because no NATO nation has suffered an armed attack by Russia, Article 20 is unavailable, leaving Article 21 by process of elimination. Hence agreeing with Pedrozo that working backward unlocks the state of affairs.

Overfield disagrees. Let’s go back to the full text of the first paragraph of Article 21 itself:

Should Turkey consider herself to be threatened with imminent danger of war she shall have the right to apply the provisions of Article 20 of the present Convention.

Overfield may or may not be correct in stating that “[i]nternational law has a well-established definition of ‘imminent threat of use of force.’” We would argue that ongoing discourse in the international law community regarding the nature of cyber and hybrid attacks evidences that this question is far from settled. Regardless of its accuracy, though, Overfield’s argument as to why Turkey cannot invoke Article 21 pursuant to such constraints is actually inapposite. It’s important to highlight that the concept of “threat or use of force” as codified in the UN Charter and attendant jurisprudence is likely untethered to Turkey’s interpretation of Montreux-related events. As such, there is no available precedent on point to guide or even check Turkish decisions in the Montreux framework.

Any legal review of wartime clause activation heretofore would be a case of subjective discretion. Those familiar with concepts of the UN charter may be tempted to apply the UN Charter’s Article 2(4) framework here, which broadly holds that nations “shall refrain in their international relations from the threat or use of force.” However, there is no codified law or precedent related to Turkey’s determination of “imminent danger” in the Black Sea that would tether its interpretations. Once again, Turkey is operating without precedent and codified standards, enabling it to be the captain of its own fate. As such, Turkey can be as sensitive to the growing warzone as it so chooses, including the belief that Black Sea maritime operations can pose a direct threat to the nation.

It is worth anchoring briefly on the potential that Turkey does explicitly invoke Article 21—appropriately so. In light of ongoing hostilities in Ukraine, some authors have already contemplated the possibility that Russia divert non-Black Sea warships through the Turkish Straits to support its Ukrainian offensive; indeed, there are already signs that Russian naval forces recently transited the Japanese Straits, suggesting that assets could already be en route to the Black Sea. This act would directly threaten Turkish sovereignty and flies in the face of Turkey’s invocation of Article 19 in late February. Thus, there is a distinct possibility that Turkey could legitimately invoke Article 21 should a perceptible Russian threat of running the Straits arise.

This possibility necessarily raises the issue of enforceability. Turkish ROE in the Straits (found in the “Joint Air and Missile Defense Directive of the Turkish Armed Forces”) does afford Turkish forces the ability to block entry of ships into the Straits who are deemed in violation of the Montreux Convention. The Directive states that ​​“Foreign warships that are found to be in violation of the rules of the Montreux Convention are blocked before entering the Straits. After entering the Straits, these vessels are accompanied or closely monitored during their passage when a situation is found to be contrary to the rules of the Montreux Convention….”

There is a dearth of historic examples wherein Turkey used force to protect “improper” transit of the Straits in violation of Montreux. In one rare example during World War II, Turkey, at the behest of Allied nations, intercepted and searched a group of German warships disguised as merchant vessels during transit of the Straits. Turkish authorities discovered various military equipment and weaponry during their search and ultimately escorted the units out of the Straits.

Checks on Turkish Invocation of Montreux Article 21

Overfield’s last remaining refuge would be Montreux Article 21’s backstop: the Convention requires support (or at least no objection) from countries party to the Convention as well as a greater international body. But upon inspection, this provision is also likely ineffective, leaving Turkey’s discretion unchecked. The operative paragraphs of Article 21 read:

Should the Turkish Government make use of the powers conferred by the first paragraph of the present Article, a notification to that effect shall be addressed to the High Contracting Parties and to the Secretary-General of the League of Nations.

If the Council of the League of Nations decide by a majority of two-thirds that the measures thus taken by Turkey are not justified, and if such should also be the opinion of the majority of the High Contracting Parties signatories to the present Convention, the Turkish Government undertakes to discontinue the measures in question as also any measures which may have been taken under Article 6 of the present Convention.

Closer inspection of the clause forecloses its safety valve. The first condition in this Clause is that Turkey’s decision can be overturned by a two-thirds majority vote of the “Council of the League of Nations.” To be sure, as Overfield points out, the United Nations (UN) adopted a Resolution in 1946 purporting to transfer powers and obligations from the League of Nations (and its organs) to itself, which he argues means “some element of the United Nations, beginning with the General Assembly, might take up the issue.” But picking up on and running with Overfield’s hedging, this is far from certain.

The Resolution begins with the following preamble: “Under various treaties and international conventions, agreements and other instruments, the League of Nations and its organs exercise, or may be requested to exercise, numerous functions or powers for the continuance of which, after the dissolution of the League, it is, or may be, desirable that the United Nations should provide.” In other words, the UN was keenly aware that some League of Nations powers may have been entrusted to a sub-organ of its body.

Yet, the UN Resolution speaks only to those powers conferred to the League of Nations as a whole: “The General Assembly will itself examine, or will submit to the appropriate organ of the United Nations, any request from the parties that the United Nations should assume the exercise of functions or powers entrusted to the League of Nations by treaties, international conventions, agreements and other instruments having a political character.” (italics omitted). A cursory textual interpretation of the resolution yields that the UN carved out a narrow path for reviewing matters formerly entrusted to the League of Nations. That is to say, UN adjudication of these cases is purposefully not guaranteed.

Nevertheless, there is precedent suggesting the UN Security Council could assume the role expected of the League Council under the Montreux Convention or, as the International Court of Justice indicated in the Namibia advisory opinion, in the exercise of its general powers under Article 24 of the UN Charter (paras 110-114). The Security Council could thus review Turkey’s invocation of Article 21 if this comes to pass.

Should Turkey refuse to obey, a sovereign may initiate a review of the Turkish decision by petitioning the UN General Assembly. The General Assembly would then likely examine the case and, should it choose, submit it for judicial adjudication by the International Court of Justice, from which the General Assembly may ask for an advisory opinion. As Tuluń notes, this process was previously activated when the “question concerning the international status of southwest Africa (today’s Namibia) had been referred for an advisory opinion to the Court by the UNGA through its resolution of December 6, 1949.” But the referral of this matter to a UN body is not mandatory and therefore Turkey’s decision may well be left unchallenged.

The final nail in the coffin may simply be the UN’s implied acquiescence to Turkey’s actions regarding the Montreux Convention to date. Turkey’s declaration that no warship, regardless of flag, could transit the Straits absent invocation of Articles 20 or 21 has yet to be discussed by the body. It is cliché to say that silence speaks volumes. But in this case, it’s true. The data points on which we rely have been public for days, and indeed the international community is attuned to what is occurring in the region, including Turkey’s actions. That no country—including Russia, who stands to lose a military advantage from Turkey’s decision to close the Straits—has requested the UN take up the issue of Turkey’s closure buttresses the idea that the body may be unwilling to dictate Turkey’s interpretations of Montreux.

In an interesting hypothetical scenario, if the matter of Turkey’s implicit invocation of Article 21 was brought to a UN vote (assuming that the UN Security Council does take up this issue as successor to the League Council), it’s feasible that the U.S., U.K. and/or France would support the challenge in an effort to curtail Article 21 restrictions on its warships.  If the Security Council successfully challenged and voided Article 21 invocation, allied warships could enter the Black Sea while Article 19 prohibitions remain in place and unchecked—restricting Russian warships from transiting the Straits.

Conclusion

The upshot is that Turkey retains wide latitude to interpret current events unilaterally. The Montreux Convention is heavy on legal ambiguity but light on historical precedent. At bottom, Turkey’s sole discretion in controlling a vital narrow sea likely yields an outsized strategic impact on allied nations during a period of hostility. For example, Turkey’s tacit “invocation” of Article 21 has, to date, succeeded in halting all warship traffic—regardless of nationality—into the Black Sea. Moreover, as we are in a pseudo-Article 21 regime it is feasible—though legally questionable—that Turkey retains the authority to open the Straits to warships of specific nations as it deems appropriate, providing a strategic military advantage for designated States. To that end, we have seen Turkey avail itself of its singular position and exercise its discretion accordingly.

Though the nation’s actions are debatably positive insofar as they mitigate escalation, the implicit or tacit invocation of its authority to do so may well be at odds with the spirit of Montreux. To realign its actions and keep the global community apprised of its thinking, Turkey should publicly and explicitly clarify its position with regard to Montreux in the coming days and weeks. To start, Turkey should provide its justification, however scant, for stretching of Article 19 to prevent all warships from transiting the Straits.

Given Turkey’s opacity to date, it would behoove the United States and NATO allies to attain a clear line of communication with the Turkish government to garner their real-time intent with regard to the Convention and plan maritime strategy accordingly. Reliance on said communications with a historically mercurial ally carries its own strategic risk for which the United States and NATO allies must account.

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Lieutenant Commander Adam Aliano is a Navy Judge Advocate currently studying at the Naval War College.

Ensign Russell A. Spivak is an intelligence officer in the U.S. Navy Reserve.

The opinions and assertions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the United States Government, the Department of Defense, or the Department of the Navy.

 

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