Two weeks after Defense Secretary James Mattis discouraged US lawmakers from blocking the transfer of Lockheed Martin F-35A fighters to Turkey, the House Armed Services Committee and Senate Armed Services Committee jointly released details of a compromise National Defense Authorization Act (NDAA) bill that would do just that.

The annual authorisation bill that sets US defence policy would block the transfer of the F-3A5 unless Defense secretary Jim Mattis submits to Congress a report on the status of the US relationship with Turkey within 90 days of enactment. The report is to include an assessment of the presence of US diplomatic and military activities within the country, and an assessment of the impact of the potential purchase by Turkey of the Almaz-Antey S-400 Triumf surface-to-air missile system.

Mattis came out against blocking the transfer of the F-35 to Turkey in a letter sent to the House Armed Services Committee Chairman on 7 July, saying that removing Turkey’s parts manufacturers from the aircraft supply chain could delay delivery of 50-75 stealth fighters for up to 18-24 months.

The NDAA bill now asks the Defense Department to study the possible removal of Turkey from the programme and come up with an alternative plan for sourcing aircraft parts in case the country is ejected from the supply chain.

In coordination with Northrop Grumman, the main fuselage manufacturer for the F-35, Turkish Aerospace Industries manufactures and assembles centre fuselages, produces composite skins and weapon bay doors, and air inlet ducts. In total, 10 different Turkish firms make parts for every F-35.

As a carrot for Ankara to abandon its interest in the Russian-made S-400 anti-aircraft system – which concerns US lawmakers and officials because of its anti-stealth capabilities – the Defense Department is also required to submit names of alternative air and missile defense systems that could be purchased by Turkey from the US or NATO allies. The US Department of State is in talks to sell the Raytheon MIM-104 Patriot system to Turkey.

Specifically, the Defense Department will be instructed to assess the operational and counterintelligence risks posed by the deployment of the S-400 to the F-35. And, it is to evaluate the impact of the Russian-made system on other systems operated jointly between the USA and Turkey, including Patriot surface-to-air missile system, the Boeing CH–47, Boeing AH–64, Sikorsky H-60 and the Lockheed Martin F-16.