Turkey and the US have raised tension over Russian made S-400 air defence systems in which Turkey is removed from the JSF programme. The deal, worth billions, is still working its way through the Foreign Military Sales process, which is subject to approval by the US State Department and the US Congress which can block deals.

"As a matter of policy, the Department does not confirm or comment on proposed defence sales or transfers until they have been formally notified to Congress," a spokesperson for the State Department said to Reuters. At the same time, the Turkish Embassy in Washington declined to comment.

Ankara's purchase of the S-400s has also triggered US sanctions. In December 2020, Washington blacklisted Turkey's Presidency of Defence Industries chief Ismail Demir and three other employees. The US authorities stated that the CAATSA sanctions over the S-400 acquisition would be wider and deeper if Turkey buys another batch. Turkish President Recep Tayyip Erdoğan said in a television interview in the US that Turkey plans to buy more S-400s. He did not meet US President Joe Biden during his New York visit. He later met Russian President Vladimir Putin.

Turkey develops its indigenous fighter aircraft with the TF-X programme. However, it still needs time to be in the inventory as the aircraft has not even made its maiden flight yet.

On the other, the bitter NATO ally and neighbour country, Greece, acquires F-35s and French-made Rafales while upgrading its F-16 fleet.