As Russia is stepping in and offering to supply turkey with SU-35 fighter jets because the united states kicked turkey out of the F-35 program. Americans made the move in retaliation to turkeys purchase of Russian S-400 air defense systems. The US says F-35 jets cannot coexist with the S-400 system which is now being delivered. Moscow and Ankara signed a two and a half billion dollar agreement for two batteries of the S-400 system in 2017. It's Russia's most advanced air defense system capable of destroying targets at a distance of up to 400 kilometers and a height of up to 30 kilometers.