This Wednesday CEO of Russian hi-tech giant Rostec, Sergei Chemezov confirmed in his in depth interview to Kommersant that Turkey, indeed, bought 4 battalions (divizion) of S-400 Air Defense System. The value of contract is $2.5 billion, with 45% of cash advance (paid) and 55% of Russia issuing a loan to Turkey--a pretty standard practice in large weapon systems purchase contracts. There is no need to go in depth about this system--it is arguably the best air defense complex in existence and it has more than enough global publicity, especially after closing Syria's skies over Russian bases there, that now there is a line to buy this weapon system. Turkey contract, however, is very special.
Make no mistakes, Russia has experience with providing NATO members with weapon systems--enough to recall deliveries of TOR-M1 Air Defense Complexes to Greece. But Turkish case is very special. Turkey is a strategic anchor for NATO's southern flank, it has largest armed forces in NATO, with the exception of the US itself, it is also hugely important regional power--so, ramifications of Turkey being increasingly pulled towards Russia, not only in some key economic fields such as nuclear energy, Turkish Stream or being present on Russia's internal consumer market, but in hi-end weaponry are immense. Well, of course Erdogan is an extremely inconvenient client and nobody really has any illusions on Turkey being perspective ally of Russia in the region, but deliveries of S-400 do change regional dynamics tremendously. After all, Turkey will be able to close her airspace to anybody, including, of course, ever moody United States. In general, Turkey gets a really strong card in her dealings with NATO (forget EU--by now only sublime believe in Turkey being accepted to EU), while Russia gets a good chunk of cash and of influence--and this is not a bad thing for Russia, once one considers that Russia already got a foothold right next to Turkey. Namely in Syria, with Putin ratifying today Russian-Syrian Agreement on the naval base in Tartus. This agreement allows Russian Navy to have in this base simultaneously 11 ships and submarines, including ones with nuclear propulsion.
I am pretty sure some former Soviet 5 OPESK (Operational Squadron) veterans who experienced all "privileges" of staying anchored in Hammamet Gulf for days "resting" (or rusting) while US 6th Fleet was having fun on its furloughs in Naples teared up now, imagining safe and comfortable conditions which Tartus will offer shortly. Tartus, of course, is not Naples (albeit, today Naples is a certified multicultural shithole) but it sure as hell beats being "parked" in the middle of Hammamet. Tartus is a lovely historic town where good booze and good food can easily be procured and many Syrians traditionally vacation there. Here is pre-war Tartus. Russian bases now sure as hell will guarantee that the place will remain peaceful for awhile and that it may, at some point of time, attract even non-military tourists.
Naval Base in Tartus allows to control Eastern Mediterranean, while the delivery of S-400 increases Turkey's degree of freedom required for very serious strategic decisions. It is a balancing act, but once one compares the mid of 2015 to the end of 2017 and how dramatically both global and regional situation changed for Russia, one may begin to appreciate a geopolitical trapeze act Russia has to perform to preserve an emerging configuration in a globally important region.