F-16 fighters flew over Ankara in order to check the work order of S-400 systems. Turkey bought these weapons from Russia, although NATO and the US stood against the deal.
"Nicholas Danforth, a senior fellow at the German Marshall Fund, said Turkey was “more committed than ever to using the air defence system it purchased.” “Turkey’s solution to this crisis has always been, ‘we activate the S-400s and Washington does nothing’,” Mr. Danforth told The National. Ankara is now “interpreting Washington’s refusal to follow through on sanctions as an endorsement of this plan", he said. “What happens when Turkey finally burns through Washington’s remarkable reserves of optimism?”, reads the story.