Following protracted efforts to purchase an air defense system from the US with no success, Ankara signed a contract in 2017 to purchase the Russian S-400s.
THIRD PART OF THE MISSILES
US officials urged Turkey to buy US Patriot missiles, arguing the Russian system would be incompatible with NATO systems and expose the F-35s to possible Russian subterfuge.
Turkey, however, emphasized the S-400 would not be integrated into NATO systems and would not pose a threat to the alliance.
Turkey has urged the formation of a commission to clarify any technical issues, but the US has failed to respond to this proposal.
Turkey continues S-400 Russian missile deployment WATCH
The US has threatened sanctions over the purchase, with Turkey responding that any sanctions would be met in kind.