Turkey's decision to buy Russian-made S 400 missile makes the United States and NATO members upset. The United States said it would terminate Turkey from a program to procure F 35 aircraft manufactured by the United States. From Ankara, it was reported that part of the S 400 missile system purchased by Turkey had started arriving in Ankara last week. Turkish President, Recep Erdogan said in Ankara that the S 400 air defense system will start functioning in 2020. The decision of Turkish President Recep Erdogan to buy the Russian S 400 air defense system has made NATO and the United States angry. Turkey is the only member of NATO that will fully utilize the Russian-made land-to-air defense system. Although Turkey's relations with NATO have begun to stiffen since last year's failed coup, President Erdogan's decision to use Russian defense technology could make relations worse. For NATO and the United States, the decision has hurt Turkey's commitment and position as a NATO ally for 65 years. The reason why Turkey finally diverted the procurement of its defense system to Russia was because the United States was slow to offer a missile defense system. While the military leaders of the United States considered that Russian S 400 air defense system is not appropriate or compatible with NATO defense systems. In addition, the United States military is concerned that the system will have an impact on the use of US F 35 aircraft. They worry that Russian technicians who will work in Turkey to accompany the use of the S 400 will steal the secret of the F 35 system. So far, Turkey has not responded to the threat of the United States which will terminate Turkey from the F 35 aircraft procurement program. The termination of Turkey from the F 35 program will certainly bring about an impact on Turkey. Because, in addition to ordering 100 units of F 35, Turkey also invests in the program, because the Turkish company has produced nearly 940 spare parts of F 35. President Erdogan's decision to buy the S400 from Russia certainly has been considered more carefully. The purchase of S 400 land-to-air missile equipment is not only about money and investment but also Turkey's determination to develop a more independent air-to-land defense. President Erdogan has taken an alternative to closer relations with Russia, as Turkish relations with NATO and the United States are strained.