Last year, after Turkey officially ordered Russia's S-400 missile system–known to Moscow as the ‘F-35 killer’–the U.S. removed it from the F-35 Joint Strike Fighter program and began taking steps to phase out aircraft parts produced by Turkey for the fifth-generation jet. It also asked Turkish students–pilots and maintainers–attending F-35 training at Luke Air Force Base, Arizona, and Eglin Air Force Base, Florida, to leave.
Turkey made a verbal agreement with Russia to purchase the S-400 in 2017 even as the Pentagon and State Department attempted to dissuade it. Turkey formally took delivery of its first S-400 system equipment in July 2019–as shown by multiple videos of the delivery to the Murted military air base northwest of Ankara.
To stop or remove something in stages.
※S-400 missile system:
An anti-aircraft weapon system developed by Russia.
In 2017, the S-400 missile system was described by The Economist as one of the best air-defence systems currently made.