OSW Commentary

The S-400 for Turkey. The crisis in Turkish-American relations escalates

S-400 dla Turcji. Eskalacja kryzysu w stosunkach turecko-amerykańskich

In late May and early June 2019, the contract for Turkey’s purchase of the Russian-made missile launchers which make up the S-400 long-range anti-aircraft missile system entered the final stage of its implementation. This has been confirmed by unequivocal statements from the Turkish leadership, the fact that the first group of servicemen (system operators) have undergone training in Russia, and the announced arrival in Turkey of the Russian technical personnel responsible for the system’s assembly. The first S-400 launchers are likely to be dispatched to Turkey as early as July (around six months sooner than the planned supply date). At the same time the US, which has blocked Turkey’s attempts to purchase anti-aircraft missile systems from Russia and China for years, is stepping up its pressure on Turkey; for example, it has announced that the unprecedented sanctions package prepared last year will be imposed if the Russian-Turkish deal is finalised.

The crisis around the S-400 is a manifestation of the deep crisis in Turkish-American relations that has been mounting for several years. More broadly speaking, it is an element of the crisis in the relationship between Turkey and the West, and de facto amounts to a major aggravation of the situation. The absence of will to make concessions on both sides makes any compromise between Ankara and Washington unlikely. At stake are the cohesion of NATO, the present and future nature of the US’s leading role, and Turkey’s place in its relations with the West and Russia. To some degree, all this affects the position of Russia, which itself is interested in undermining the positions of NATO and the US.


The modernisation of Turkey’s air defence

Since the 1970s, the ground component of Turkey’s air defence has been the American-made long-range MIM-14 Nike-Hercules missile launchers manufactured a decade earlier. Since the 1990s the Turkish military has constantly raised the need to replace them with new-generation armaments, but for many years the only option under consideration was the American-made MIM-104 Patriot missile systems, which were treated as the technological base for the development of Turkey’s armament programmes. The lack of progress in this matter resulted in the announcement in 2009 of an open tender for anti-aircraft missile systems, in which the main parameters included price, punctuality of supply and access to technology. The bidders that took part in the tender included American (Raytheon and Lockheed Martin), Chinese (CPMIEC), Russian (Rosoboroneksport) and European companies (Eurosam), with the Chinese finally winning the tender in 2013. It is worth noting that the only document signed was a preliminary agreement, which the Turkish side saw as an element of pressure on Washington. Under pressure from the US, the contract with China was suspended and then cancelled (2015), and NATO’s Patriot launchers were temporarily relocated to Turkey (2012); this was directly related to the escalation of the war in Syria and the involvement of NATO states’ forces in this conflict. However, Turkey’s attempts to finalise the purchase of the Patriot systems on conditions favourable to it failed. These conditions included access to the most recent version of the system, access to technology, as well as a price Ankara would consider reasonable.

For many years the only option for Turkey has been to purchase American Patriots as part of the modernisation and development of its air defence system.

The absence of progress in negotiations with Washington, the deterioration of Turkish-American relations (caused, among other factors, by the US backing the Syrian Kurds and the Turkish opposition), as well as Turkey’s closer cooperation with Russia over Syria, all gave an impetus to reviving the idea of purchasing the Russian-made S-400 systems to serve as a transitory project (and as an instrument of pressure in negotiations) in the process of obtaining the Patriot systems. The agreement to purchase the S-400 was concluded on 28 April 2017, and the contract was signed on 12 September that year. Russia committed itself to deliver four S-400 batteries to Turkey by the end of the first quarter of 2020. The contract’s estimated value is US$2.5 billion. The total number of missile launchers covered by the contract has not been made public, although it should be assumed that the number will be 16 (the basic variant based on the Russian model) or 24 (the maximum variant used by the militaries of NATO states)[1].

From the beginning, Moscow has viewed the contracts to supply the S-400s to Turkey as a matter of prestige. Until February 2019, work had progressed according to the adopted schedule with no problems arising (unlike in the case of the contract to supply S-400s to China), and in spring 2018 it even accelerated. Back in March 2019, Hulusi Akar, Turkey’s defence minister, announced that the supplies would commence in October (as initially planned); however, a month later both sides suggested that the contract’s implementation would accelerate, and the supplies would commence in July. According to announcements made in May 2019 by Ismail Demir, the head of Turkey’s Defence Industries holding,  the supplies are likely to commence as early as June. However, at the beginning of June Sergey Chemezov, the head of the Russian company Rosoboroneksport, which is responsible for the contract’s implementation, said that the supplies will begin “in two months”[2]. The decision to launch the supplies may be taken at literally any moment. The launchers that will form elements of the first S-400 battery to be delivered to Turkey are ready for dispatch, the military personnel who will serve as system operators have undergone training (they travelled to Russia in late May for this purpose), and a date has been set for the technical personnel (representatives of either the manufacturer or the Almaz-Antey Air and Space Defence Corporation) to arrive in Turkey in late June to supervise the final stage of assembly and configuration of the armaments and battery equipment. According to the new schedule, all the S-400 systems ordered by Turkey are expected to be delivered before the end of 2019.

Although the Turkish leadership have ruled out the possibility of the contract being cancelled, they are conscious of the pressure from the US and NATO, and for many months have carried out an information campaign to assure the public that the contract’s implementation is not at risk. Ankara has announced its readiness to supervise the launchers jointly with its allies, and is ready to guarantee that no Russian personnel will be allowed to operate the S-400s delivered to Turkey. Alongside this, it continues to be interested in purchasing American-made Patriot systems in the future. These moves have not been well received by Washington; according to the Turkish side, the Americans have not expressed any interest in the proposed appointment of a bilateral or broader (NATO-wide) team to dispel the doubts the allies have expressed.


Turkey’s political situation

Both the purchase of the S-400s and Turkey’s relations with the US and Russia are elements of a more comprehensive background determining the changes that have been taking place in Turkey’s foreign and domestic politics. In this context, the first and fundamental process is the thorough internal overhaul of the state which has been carried out since 2002 by the AKP and President Recep Tayyip Erdoğan, combined with intensive modernisation and a desire to play the main role both in Turkey’s immediate neighbourhood and on the wider international scene. To these ends, the country’s political priorities include boosting its military potential and the intensive development of its high-technology economy, and the modern S-400 anti-aircraft missile system is one example of this. Another is Turkey’s involvement in the American-led project to develop the F-35 multi-role combat aircraft (see below). Ankara’s tough stance results from the frustration of Turkish politicians and Turkish society over the secondary role the country is playing in the relations with its strategic (Western) allies (in this case the US), but also in its relations within NATO and with the EU. From the Turkish perspective, the US has been ignoring Turkey’s modernisation ambitions, Turkish interests in the Middle East (the fact that Washington did not consult with Ankara on issues such as its invasion of Iraq, its policy towards the Arab Spring, the Israeli-Palestinian conflict, Iran etc.), the Cyprus issue; finally, the US has been carrying out actions that stand in sharp contrast to Turkey’s interests. Examples of the latter include Washington’s consistent support for the Syrian Kurds (who in Ankara’s opinion represent the Syrian wing of the terrorist Kurdistan Workers’ Party), and for the Gülen movement, which Ankara accuses of having organised the failed coup d’état in 2016 (Gülen resides in the US; Washington has not only ruled out his extradition but has also continued to actively criticise Turkey’s domestic situation).

From Turkey’s perspective, the US has been ignoring Turkey’s modernisation ambitions, and has taken actions which conflict sharply with Turkish interests.

Turkey’s sense of being exposed to Washington’s destabilising actions is one particularly sensitive element of Turkish-American relations. This was hinted at during the mass protests around Gezi Park (2013), and was more openly suggested during the failed coup of 2016, as well as in the context of Turkey’s imprisonment of American pastor Andrew Brunson, who was accused of having contact with the coup’s perpetrators (in August 2018 the US and others imposed sanctions on Turkey in response). Turkey is aware of the US’s objective ability to destabilise its capital markets, as manifested in August 2018 in connection with the Brunson issue; this is of particular importance in the context of Turkey’s present economic recession and its tense political situation (the ruling AKP’s relative failure in local elections in March 2019, and the controversial decision to re-run the election in Istanbul on 23 June 2019). Another factor weakening Turkey’s ties with the West involves the consequences of the large-scale purges carried out in the Turkish military following the 2016 coup attempt. These mainly affected officers who had been in contact with partners from NATO armies for many years, and so the purge has considerably undermined both confidence in the Turkish army and the informal channels of communication.

From Washington’s perspective, Turkey has been consistently and irreversibly dismantling the American political system in the region, which Russia has been taking advantage of.

The tension in Turkish-American relations has been accompanied by a thorough revision of Turkish-Russian ties. Since the outbreak of the civil war in Syria, these relations have teetered on the brink of open armed conflict (for example due to the downing of the Russian Su-24 jet in November 2015), in which Turkey (which sees itself as having been abandoned by its allies) shifted its position to become Russia’s partner in Syria (the two states cooperated in northern Syria), deepened its strategic economic cooperation (for example by signing a contract to construct the second (after Blue Stream, commissioned in 2005) gas pipeline, TurkStream, in 2016) and strategic military cooperation (the contract to purchase the S-400 signed in 2017). On the one hand, Turkey’s cooperation with Russia involves isolated tactical initiatives, is burdened with multiple-level tensions and is only temporary in nature (especially as regards Syria). Moreover, it is beyond doubt that this cooperation may be viewed as a bargaining chip in Turkey’s relations with the US. On the other hand, it is developing at the same pace as Turkey’s relations with the West are deteriorating, accompanied by increasing anti-American sentiments and a revival of Turkish nationalism (which very well matches the Eurasian ideas promoted by Russia), and finally by major tension in relations between Russia and the US (for example over the conflict in Ukraine, and Russia’s involvement in the US presidential elections in 2016). In this context, Ankara’s rapprochement with Moscow is being viewed (both in Turkey and elsewhere) as a strategic alternative to its former pro-Western orientation.



Washington’s hard-line stance

The United States has expressed a clearly negative opinion on Turkey’s purchase of Russian-made anti-aircraft defence systems (as well as another system manufactured by a non-NATO state, as evidenced by the developments surrounding the tender won by the Chinese company CPMIEC). This stance is convergent with Washington’s overall assessment of Turkey.

Its formal basis is the sharp objection to Turkey purchasing equipment that is not compatible with NATO systems, as well as the fear that by retaining at least partial control of the launchers delivered to Turkey, Russia may be able to read information provided by the most advanced American-made jets delivered to Turkey, learn the details of their design and construction, and then devise effective tactics to combat them. The US has also voiced sharp criticism as regards the prospect for cooperation between Turkish companies and Russian suppliers which have been covered by sanctions imposed on Russia in connection with the war in Ukraine. The upcoming implementation of the contract to purchase the S-400s has significantly boosted the US’s campaign targeting this project. This campaign’s elements are as follows:

  • threatening to use the Countering America’s Adversaries Through Sanctions Act (CAATSA; 2017) against Turkey, to impose sanctions on companies that cooperate with Russian intelligence services and the armaments sector (Section 231);
  • suspending the transfer of the F-35 combat jets purchased by Turkey (the transfer of F-35 jets was de facto suspended in August 2018; the decision connected with the S-400s was confirmed in April 2019), political declarations and legislative measures intended to exclude Turkey from the project involving the construction of F-35s (Turkey has been involved in this project since 2004, and has invested around US$1.25 billion in the production of 100 jets, 30 of which have already been ordered; elements of the jets’ fuselage, undercarriage and cockpit equipment are manufactured in Turkey);
  • threatening to suspend cooperation, technology transfer and the supply of spare parts for the Turkish military and its armaments industry, which would be targeted at Turkish companies involved in production and the Turkish military’s planning process regarding the purchase of CH-47F Chinook and UH-60 Black Hawk helicopters, F-16 jets, and finally the Turkish T129 Atak helicopter, which is built with the use of American-made components and technology, and is exported to Pakistan and other countries. Regardless of the problems American companies would face (the need to transfer production activities outside Turkey), the costs of these actions for Ankara are estimated at US$10 billion.


Alongside the planned activities directly connected with the S-400, in recent weeks the US Congress has resumed work on drawing up sanctions to be imposed on Turkey (Turkish officials and politicians) in connection with the fear that the civil rights of Americans in Turkey may be threatened (this is a reference to the sanctions imposed in 2018 in connection with pastor Brunson’s imprisonment). The Department of State, for its part, has withdrawn its conditional consent to Turkey importing oil from Iran, and has offered sharp criticism of Turkey’s attempts to explore natural gas fields on the Cyprus Shelf. The pressure was to be crowned by an informal ultimatum from the Department of State setting the date for Turkey’s withdrawal from its planned acquisition of the S-400s for 9 June 2019. Two days before this deadline, citing Patrick Shanahan, the acting US Secretary of Defence, American media reported that the Pentagon had communicated an ultimatum to Turkey according to which the deadline for excluding Turkey from the F-35 programme was set for 31 July. If Ankara ultimately does not formally abandon its purchase of the S-400s, after this date the training of Turkish servicemen currently residing in the US will be cancelled (it has already been suspended). The first group of officers included 42 individuals; the US has refused to accept another group composed of 34 pilots and ground service specialists who were expected to arrive in the US to take part in training in the second half of 2019. The participation of Turkish companies in the F-35 programme is to end by 2020.

In this deep crisis in Turkish-American relations, Moscow has been effectively leading Ankara to think that it can present an alternative and a counterbalance to the US.

The above-listed activities, alongside media reports regarding Turkey’s current economic problems (including a recession, the absence of reserves and its dependence on foreign loans), should be viewed as an element for putting pressure on Turkey, in order to make it sensitive to American economic pressure and undermine its credibility in the eyes of investors and lenders. Against the backdrop of American pressure, suggestions to resolve the dispute by achieving a relative compromise were almost silent: an offer to sell the latest version of the Patriot system at a slightly more attractive price, combined with a gradual redeployment of NATO batteries, was reiterated in February 2019.

The determination with which the US is putting pressure on Turkey seems surprising in the context of the doubts that have emerged regarding some of the formal reservations concerning the S-400 systems purchased by Ankara. The main doubt relates to the fact that the F-35s used by Israel and Norway are at present being tracked by Russian radars which are elements of the S-400 systems located in Syria and Murmansk oblast respectively. Another doubt – in the light of available information – is the fact that Russia usually transfers full control of the system to the purchaser (in the case of American-made launchers, the manufacturer retains some degree of control over them). Due to the nature of the transaction (Russia does not sell systems which are identical to those its own armed forces use), it cannot be ruled out that – driven by political and strategic motives (disrupting NATO’s coherence) rather than military and technical motives (expanding the field of surveillance over a potential enemy) – Moscow is indeed ready to give Ankara full control of the launchers it sells to Turkey[3]. It is beyond doubt that one important motivation for Washington’s determination is the US’s rivalry with Russia on the market for high-technology armaments: in this case, Turkey’s purchase of the S-400s boosts the system’s prestige and increases its market attractiveness (in October 2018 India signed a contract to purchase S-400s, although it had previously been interested in buying Patriots; at present Washington is making threats of sanction to the government in Delhi as well). For the US, from the military point of view, the fact that its ally Turkey has purchased a technologically advanced armament system over which the US army will have no control may be a problem, especially as both states’ military involvement in the Middle East is increasingly divergent (it is Turkey, rather than Russia, that may use the S-400s to spy on the Americans).

The dispute over the S-400 may result in Turkey’s withdrawal from its commitments to NATO, at least in matters related to Russia.

The US’s stance is easier to understand in the context of the accusations which the American leadership has been levelling against Turkey for years. Since at least 2003, Washington has expressed its irritation at Ankara torpedoing the US’s Middle Eastern policy. This included Turkey’s objection to the US-led intervention in Iraq; its periodically blocking the activity of the US base in İncirlik; its fight against the Kurds (who are the US’s main client in Syria); its confrontational approach to Israel, Saudi Arabia and Egypt; its cooperation with radical Muslim organisations; its (limited) cooperation with Iran, etc. Turkey’s domestic policies have also triggered serious disquiet in Washington and among the American public. These policies include violations of civil rights (especially in relation to US citizens, Turkish military officials, journalists, Kurds, and individuals accused of being linked to Fethullah Gülen). Other issues include Turkey’s closer cooperation with Russia in order to challenge American interests in Syria; to undermining the US’s moves to tighten its policy towards Russia over Moscow’s aggression against Ukraine; and to counter the anti-Russian mood in the Congress and the media which have been reinforced by the accusations that Russia meddled in the US presidential campaign in 2016. From Washington’s perspective, Turkey is disassembling the American political system in the region, while itself becoming the subject of Russia’s game. According to Washington, Ankara is doing so in a conscious, consistent manner which will prove irreversible in the current political landscape. The S-400 issue seems to be not so much the cause of the crisis as a catalyst for a new stage of it.


Russia’s game

Russia is playing a game focused on Turkey’s ambitions and on the deep crisis in Turkish-American relations in an exceptionally skilful manner. At the same time, it is stoking the tension and effectively building a conviction in Ankara that Russia is the alternative and counterbalance to the US. Alongside this, Moscow is trying to maintain an appearance of altruism and an at least tactical complementarity of the policies pursued by the two states, especially against the backdrop of differences between Turkey and the West. Russia’s attractiveness for Ankara was demonstrated during the two states’ cooperation in Syria (regardless of the actual blockade of Turkey’s expansion in the region and its constant reduction of the influence built up by Turkey), in Russia’s support for Turkey’s domestic policy (for example, in the context of Western criticism regarding the purges carried out following the attempted coup in Turkey), and in the prospect of economic benefits (such as the cooperation in the gas sector that has brought financial benefits to the new ruling elites in Turkey). The contract for the sale of the S-400s to Turkey – which Russia is implementing on favourable financial terms and according to a highly preferential schedule – is an excellent example of this trend. Another example is Russia’s suggestion (voiced in tandem with Washington’s subsequent threats) regarding Turkey’s participation in the development of the design, production and its subsequent purchase of the Russian fifth-generation Su-57 multi-role combat aircraft and the latest S-500 air defence missile systems (in May 2019 President Erdoğan announced Turkey’s intention to take part in the project). Ankara increasingly views its cooperation with Russia as an opportunity to solve its current problems, and treats Russia as a reliable supplier of anti-aircraft defence systems, should the contract for the S-400s be implemented. However, at the same time, this cooperation considerably reduces Turkey’s strategic importance; a mere four launcher batteries will not meet Turkey’s needs, and pose a risk that Turkey’s defence cooperation with the US may be cancelled (Turkey continues to hope that in the end it will purchase the Patriots). Moreover, Turkey’s contract with Russia risks additional financial problems for Turkey (the threat of a freeze on current investments in cooperation with the US). Another important problem is the risk of financial problems for Turkish companies from the armaments sector, should sanctions be imposed; also, the risks connected with the overall economic slowdown in Turkey may increase. As for Russia, regardless of its temporary profit from the sale and promotion of the S-400s, with its actions it is coming increasingly closer to achieving its strategic goals, which include building influence in Turkey itself, undermining NATO’s coherence (the Turkish army is NATO’s second biggest after that of the US) and disassembling an American network of alliances, ties and dependencies, in this case in the Middle Eastern region.



As the process of Turkey purchasing the S-400 system is now well-advanced, the interested parties have adopted a hard-line stance, and considering the pressure from the public and the elites in both Turkey and in the US, we should expect the contract to be finalised in the coming weeks. For Turkey, this would mean a significant strengthening of its own military capability, which would for example translate directly into its activity in Syria targeted at the local Kurds (although this would be combined with the risk of heightened tension with the US troops who are de facto protecting the Kurds). At the same time, the contract’s finalisation would mean more opportunities for cooperation with Russia in almost any field. However, it is very unlikely that the temporary benefits for Turkey could translate into stable trends: for example, due to the US’s overall approach, the power of its instruments and Turkey’s domestic limitations (economic problems on the one hand and its asymmetric approach to Russia on the other).

In the context of the US Administration and the Congress’s tough stance and determination, we should expect the immediate imposition of sanctions against Turkey (this is what happened during former crises, and would be in line with current pronouncements), as well as a considerable rise in anti-American sentiment within Turkey. With regard to possible retaliatory measures, it is very likely that Ankara will try to use the limitations on the US using military infrastructure in Turkey as an instrument to put pressure on it; this will primarily involve the base at İncirlik, which is extremely important for the US’s actions in the Middle East. Regardless of how effective the long-term, US-led sanctions against Turkey are, Washington has the tools to hit Turkey’s economic credibility and the Turkish lira, a move which may trigger an escalation of socio-political tension in Turkey (a more destructive variant of the events that happened in August 2018). The US has de facto control over a range of instruments that could destabilise Turkey’s domestic situation, and may be willing to use them either consciously or not.

Even if a very unlikely compromise is reached (the supplies of the S-400s are suspended and control of them is transferred to the NATO allies) the potential for further Turkish-American tension remains unchanged (Turkey’s domestic situation, the Kurds), just as retaliatory measures from Russia targeting Ankara are equally likely (e.g. the crisis over the Syrian province of Idlib).

At present, the Turkish issue is the most important test of the US’s leadership of NATO. Combined with the uncompromising American stance, Turkey’s ambitions and frustrations (stoked by Russia) affect the relative cohesion of NATO both in relation to Russia (which is viewed as an enemy to greater or lesser degrees) and in the Middle East. Restoring confidence between the US & its allies and Turkey would be a lengthy and difficult process. It is more likely that Turkey will withdraw from its allied commitments under NATO, at least in matters relating to Russia. In the worst-case scenario, the tension will escalate: the threat of incidents in the Middle East will increase, and most importantly, the current situation will trigger a destabilisation of Turkey’s domestic situation.


Appendix. The S-400 anti-aircraft defence system and its users

The S-400 ‘Triumph’ long-range anti-aircraft missile system is manufactured by the Almaz-Antey Air and Space Defence Corporation. According to available information, it enables reconnaissance, tracking and destruction of all types of air attack (aircraft and missiles) in conditions of active radio-electronic warfare and other jamming measures. The S-400 missiles can strike aerodynamic targets (aircraft and cruise missiles) at distances of 2–400 km (confirmed successful strike using a 40N6E missile at a distance of 380 km) and ballistic missiles (rockets) at distances of 5–60 km, which are moving at speeds of up to 4.8 km/s, at heights of 5 m – 35 km. The radio-location and guidance stations (of a battalion set or battery) enable concurrent tracking of up to 160 targets and shooting of up to 80 targets.


The Russian Aerospace Forces are the main users of the S-400. The first systems were purchased in 2007, and the spring of 2019 saw the end of the process of shifting to the S-400s within the State Armaments Programme (Russian: GPV), which had been planned to close by 2020. 28 regiments (56 battalions) are equipped with S-400s, covering 448 launchers and 1792 missiles in total. The Moscow and Kaliningrad oblasts are the regions with the biggest number of this type of armaments. Outside Russia, there are two battalions equipped with S-400s that cover the Russian bases in Syria (Khmeimim and Tartus).

China is the first non-Russian user of the S-400s. A contract worth US$3 billion was signed in April 2015, and the first of four regiment sets was delivered in January–May 2018. Delivery of another regiment set is planned for 2019. The implementation of the contract with China has been delayed, and is subject to obscure problems concerning the supply of missiles.

India is the third state (after Turkey) to have signed a contract for the delivery of S-400s (in October 2018). It intends to equip 5 regiments with the system (80 launchers), and the total value of the contract is estimated at US$5 billion.

Saudi Arabia announced a preliminary decision to purchase S-400s in 2017, although under pressure from the US the negotiations have been suspended.

According to unofficial information, Russia has refused to sell S-400s to Iran. It is possible that this announcement was an element of deliberate disinformation on Russia’s part; this seems all the more likely because the announcement was made in late May 2019, during the period of the US’s increased pressure on Turkey. The same can be said about the announcement by the Iraqi ambassador in Moscow (also made in May 2019) regarding the Baghdad government’s alleged decision to purchase the S-400 system.

[1] An anti-aircraft battery is composed of 4 to 6 launchers (in the case of the S-400, each contains 4 missiles), a radio-location station, a guidance station, a command vehicle, and support and protection vehicles.

[2] ‘РФ начнет поставки С-400 Турции через два месяца, системы уже произведены – Чемезов’, Интерфакс, 7 June 2019.

[3] It is unlikely that the Turkish army would approve an armament for operation which had not been tested for the presence of spying devices used by a third party (which does not rule out the possibility that Russia might have attempted to install such systems in the S-400). One of the most important factors for Turkey, when it considered the purchase of Patriots, was that it should have full autonomy in using them. In the case of the purchase of the S-400s, it is more likely that Russia agreed to implement the contract on conditions favourable to Turkey (both in the military-technical and the financial aspect) because it viewed this as primarily a politically-motivated undertaking that would weaken of the relations between NATO’s two biggest armies and deepen the current divides within NATO. It is worth noting that Russia has other means of radio-location and radio-electronic reconnaissance in the Black Sea basin and in the eastern part of the Mediterranean Sea basin (including the S-400 units deployed in Syria).