ALLIES: DOD concerned by Turkey purchase of Russian air defense system.

The Pentagon is concerned by Turkey’s decision to buy a Russian air defense system, Defense Department spokesman Jeff Davis said Monday.

Davis said that Defense officials “certainly are aware of the reports” that Turkish President Recep Tayyip Erdoğan is currently in talks with Russia to buy the S-400 surface-to-air missile system.

“Our only concern about it is one of interoperability,” Davis told reporters at the Pentagon. “Turkey is a NATO ally. Generally speaking, it’s a good idea for allies to buy interoperable equipment.”

Interoperability depends on with whom one wishes to interoperate.