The U.S. Defense Department has given Turkey one last chance to cancel its planned order of the Russian-made S-400 surface-to-air missile system before it begins removing the NATO ally from the F-35 Joint Strike Fighter program.
In a letter sent to Turkish Minister of Defence Hulusi Akar, Acting Defense Secretary Patrick Shanahan on Thursday outlined a list of actions the U.S. will begin taking to suspend Turkey's participation in the F-35 program starting July 31.
"This timeline will enable many, but not all, Turkish F-35 students currently in training to complete their courses prior to departing the United States by July 31," Shanahan said in the letter obtained by Military.com. The news was first reported by Foreign Policy.
"We have also informed the Ministry of National Defense that we do not recommend starting any new training programs for Turkish personnel on the F-35 in the United States as we anticipate they would be recalled in the near future," he said.
Shanahan said the parameters also restrict Turkey from participating in the annual F-35 Chief Executive Officer Roundtable on June 12.
The acting defense secretary noted that Turkey's procurement of the S-400 hinders its ability "to enhance or maintain cooperation with the United States and within NATO."
The Defense Department will remove all Turkish personnel from the F-35 Joint Program Office no later than July 31. "At this point, all Invitational Travel Orders (ITOs) and/or Common Access Cards (CACs) will be canceled, and Turkish Air Force personnel will be prohibited from entering JPO facilities," the letter states.
"You still have the option to change course on the S-400," Shanahan said.
Under Secretary of Defense for Acquisition and Sustainment Ellen Lord reiterated that sentiment Friday, saying that Turkey's removal from the program is reversible should it comply with the U.S.' request.
Lord, speaking to reporters at the Pentagon, cited the long-standing partnership between the U.S. and Turkey, stating that relations remain strong as U.S. Air Force pilots are gearing up to train alongside Turkish pilots in the upcoming Exercise Anatolian Eagle.
But "further activity could accelerate" the U.S. move to remove Turkey from the F-35 program, she said.
Turkish President Recep Tayyip Erdogan has said that his country -- which hosts Incirlik Air Base, a key Air Force hub -- will not reconsider its plans to purchase the S-400 SAM system, nicknamed the "F-35 killer" by Moscow.
Turkey's Foreign Minister Mevlüt Çavuşoğlu said in April that the S-400 procurement is a "done deal."
While the Pentagon has repeatedly stressed the looming incompatibility issue that threatens the F-35 program should Turkey proceed with the S-400 purchase, the new line in the sand from U.S. officials stems from training the Turks have begun receiving in Russia on the SAM system, Lord said.
"The U.S. was disappointed to learn that Turkey sent personnel to Russia to train on the Russian system," she said.
"The S-400 is incompatible with the F-35," Lord said. "We do not want to have the F-35 in close proximity to the S-400 over a period of time because of the [system's] ability to understand the profile" of the jet.
The Pentagon announced April 1 that it had halted shipments of F-35A stealth fighter equipment to Turkey after it refused to cancel the S-400 purchase.
But Luke Air Force Base, Arizona, accepted its third and fourth F-35 jets for the Turkish pilot training program that same week.
Two Turkish instructor pilots have completed training, with four students currently in training, Maj. Rebecca Heyse, 56th Fighter Wing spokeswoman, told Military.com on Friday.
There are now a total of 42 students -- pilots and maintainers -- attending F-35 training in the U.S. at Luke and at Eglin Air Force Base, Florida, according to the Pentagon.
Lord said Friday that the Pentagon is looking to U.S. suppliers to potentially replace production on parts that Turkey makes for the Joint Strike Fighter program, adding that discussions are ongoing.
Turkish industries produce 937 parts for the F-35, including items for the landing gear and fuselage, she said.
Discussions between the plane's manufacturer, Lockheed Martin, and engine manufacturer Pratt & Whitney to find alternate sources are "well underway, but [nothing] has been finalized," Lord said.
“Managing a program of this scale and complexity, we are constantly evaluating the supply chain for risks and continue to develop plans that ensure continuity in production," said Mike Friedman, a Lockheed spokesman. "Our team is committed to minimizing any impact to the program so that we can continue to deliver and sustain this transformational capability for all F-35 operators."
Turkey is expected to begin installing its S-400 system next month. F-35 deliveries to Turkey had been slated to occur between late summer and the end of the year.
In an effort to keep Turkey from buying Russian-made weapons, the State Department in December approved the potential sale of the Patriot missile system and related equipment to the country for $3.5 billion.
Lord and Andrew Winternitz, the acting principal director for Europe and NATO Policy at the Pentagon, said the Patriot sale is still an option.
Turkey, however, has said the system is insufficient for its needs. When asked why it would need the S-400, which has increased range and increased sensor sensitivity, Winternitz said, "Turkey is obviously in a very tough neighborhood.
"I think they face threats from a number of places, but they have identified this as a security need. We are willing to discuss with them a solution that does not involve the S-400," he said.
The officials said that the F-35 program's intellectual property is not at risk.
"We control what is downloaded from our computers; we have shared what's appropriate. The Turks have no critical documentation that we are concerned about," Lord said.