On May 28, Reuters reported that  U.S. officials are considering suspending F-35 training for Turkish pilots as Turkey continues to move forward with its plans to purchase Russia’s S-400 and and missile defense system. The delivery of F-35 equipment to Turkey was previously halted in late March due to U.S. objection to the planned purchase. As Turkish military personnel receive training in Russia for the S-400 program, Turkish pilots continue to receive F-35 training at Luke Air Force Base in Arizona. U.S. officials argue that Turkey’s deployment of the S-400 deployment poses a threat to the F-35 program.