After months of warnings, the United States said that Turkey's decision to buy Russia's S-400 missile system was incompatible with  the  US warplane program. "Until they forgo delivery of the S-400, the United States has suspended deliveries and activities associated with the stand-up of Turkey's F-35 operational capability," Pentagon chief spokesman Charles E. Summers Jr. said. US officials have voiced concern that, with Turkey in both camps, Russia could obtain F-35 data to improve the accuracy of the S-400 against Western aircraft. Turkey had planned to buy 100 F-35A fighter jets, with pilots already training in the United States. The plane's manufacturer, Lockheed Martin, said that contracts with Turkish companies to build parts for the F-35 had been expected to reach 12 billion USD.