About 100 Turkish servicemen will be sent to Russia in late May to learn how to operate the S-400 air defense systems that Ankara is buying from Moscow, a senior military source in Ankara told Sputnik Tuesday.

AVA- “In late May, about 100 of our servicemen will go to Russia for a training on S-400 operation,” the source said.
Russia and Turkey closed a $2.5 billion loan agreement for the shipment of a total of four batteries of S-400 systems in December 2017. The first delivery is slated for July 2019.
The United States has repeatedly voiced its objection against the purchase of that systems by Turkey citing their incompatibility with NATO military equipment. Washington threatened to halt the support for F-35 jets if Ankara proceeds with the purchase of S-400s.
Ankara stressed on multiple occasions that S-400s do not threaten US-manufactured F-35s in any manner, underlining that the purchase of the systems was Turkey’s sovereign affair unrelated to the security of the alliance.