Ankara will have trouble maintaining military-to-military ties with Washington and other allies once it procures the cutting-edge S-400 anti-aircraft missile systems from Moscow, the Defense Department has warned. Speaking to TASS, Pentagon spokesman Eric Pahon said the US understands that Turkey wants to upgrade its air defenses, but ramifications will follow. The country will begin deployment of the first S-400 squadrons in October this year, according to local defense officials.