After years of negotiations, the U.S. authorities finally began the process of excluding Turkey from the F-35 program due to its decision to acquire the Russian S-400 air defense system. Russia reacted by offering Turkey to buy its Sukhoi Su-35 fighter jets instead.

“The United States and other F-35 partners are aligned in the decision to suspend Turkey from the program and initiate to process to formally remove Turkey from the program,” said Undersecretary of Defense for Acquisition and Sustainment Ellen Lord, adding that she would work with the Joint Program Office and other F-35 partners to quickly unwind Turkey's participation.

By March 2020, the industrial participation of Turkey in the F-35 program will be completely withdrawn from the supply chain. This should cost $9 billion over the life of the program, with most of the affected parts production being distributed among U.S. companies. “Over the last several months we’ve been working to establish alternative sources of supply in the United States to quickly” bounce back said Lockheed Martin spokeswoman Carolyn Nelson, quoted by Reuters. Despite the disruption, the company says it should meet its goal of delivering 131 aircraft in 2019. As for the hundred F-35A fighter jets ordered by the Turkish Air Force, they have yet to find a new operator.

The Turkish Foreign Ministry denounced a “unilateral step [that] is incompatible with the spirit of alliance and does not rely on any legitimate justification”. It calls for the United States to reserve the decision that will “cause irreparable wounds in our strategic relations”. “The fact that our proposal to establish a working group with the participation of NATO in this regard is left unanswered is the most obvious indicator of the prejudice on the US side and the lack of the will to resolve the issue in good faith,” added the Turkish diplomacy.

After being refused by the Congress a transfer of technology for the Patriot missile system in 2009, Turkey had initially shifted its attention to China and its Hongqi-9/FD system. But negotiations did not succeed, and eventually, the country ordered the S-400 Triumph from Russia, in a contract valued at $2.5 billion in 2017.

Based on the Countering America’s Adversaries Through Sanctions Act (CAATSA) which was enforced following Russia’s involvement in Ukraine and Syria, Washington warned Ankara that the delivery of S-400 systems meant the exclusion of Turkey from the F-35 program and could even lead to sanctions. 

The United States also voiced its concern that integrating the S-400 and the F-35 in the same system could compromise sensible information regarding the aircraft. “The F-35 cannot coexist with a Russian intelligence collection platform that will be used to learn about its advanced capabilities,” justified the White House press secretary in a statement.

Measures were gradually taken to support those threats. In April 2019, the Pentagon announced that "deliveries and activities" related to the Turkish F-35 operational capability were suspended. In June 2019, the US military announced they would suspend the year-long training of four Turkish pilots at Luke Air Force Base, Arizona, if Ankara did not renounce buying the S-400 by July 31, 2019.

Yet Turkey decided to proceed with its order and received the first parts of the S-400 on July 12, 2019, prompting the U.S. authorities to react.

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After halting the delivery of parts earlier in 2019, the Pentagon is now considering halting the training of Turkish pilots on the F-35 in yet another episode of the ongoing dispute between the United States and Turkey regarding the acquisition of the Russian S-400 system by the latter.
 

The White House tried to defuse the situation by claiming that “as NATO Allies, our relationship is multi-layered, and not solely focused on the F-35. Our military-to-military relationship is strong, and we will continue to cooperate with Turkey extensively, mindful of constraints due to the presence of the S-400 system in Turkey”. However, with several other NATO member states operating the F-35 aircraft, one can wonder how joint exercises and operations will be conducted with Turkey if both systems cannot cooperate.

Meanwhile, the Russian government through the Rostec state corporation said it was ready to provide Turkey with an alternative, the Su-35 fighter jet. “If our Turkish colleagues express a desire, we are ready to work out the deliveries of the Su-35,” said Sergey Chemezov, head of Rostec.