For reasons explained repeatedly by Turkish officials, such as competitive cost advantage, technology transfer and capabilities, Turkey appears to be seriously considering buying Russian S-400 missile defense systems.

The U.S. and NATO repeatedly expressed their concerns about the sale, underlying the interoperability problems that would arise when the system comes into force. Of course this is also mainly a political question for Washington with regard to Turkey's foreign policies and its recent preference to be more independent when it serves its needs better.

To alleviate this question, President Recep Tayyip Erdoğan underlined the fact that another NATO country, Greece, has had a Russian-made S-300 defense system since the late 1990s. Greece received the systems from Cyprus after a deal brokered by the U.S. to satisfy Turkey's objections at the time. However, Greece eventually integrated this system into its national defense system following a military exercise called "White Eagle" on December 2013, according to Mustafa Kibaroğlu, chairman of the Political Science and International Relations Department at MEF University in Turkey. So, the system is not rotting away somewhere in Crete. It is indeed in use.

Pentagon spokesman Johnny Michael told me that over the years the U.S. had expressed its concerns to Greece that the system is incompatible with their commitments to the NATO alliance to fund the upkeep of a legacy system such as the S-300. The Pentagon's concerns are in line with the reports that Greece sought to buy new S-300 missiles from Russia in 2015, asking Moscow to do the maintenance work.

Still, U.S. officials wouldn't budge from their criticism of the Turkish decision to buy a Russian-made system. A spokesman for the U.S. State Department, speaking on condition of anonymity due to diplomatic protocol, brought up the commitment made by NATO allies in the 2016 Warsaw Summit, "to enhance the resilience by working to address existing dependencies on Russian-sourced legacy military equipment through national efforts." This is indeed a commitment that senior Turkish officials are having a hard time explaining.

But, Turkey and the U.S. should focus on the benefits that might come from a NATO member owning the most advanced Russian defense system. How?

"There are Russian systems in other NATO countries, not the S-400 system, and it ends up being more of a problem for the Russians. They actually incorporate those systems into NATO exercises and tests. It is not a positive thing for Moscow to have that happen for their newest and shiniest toy," Naz Durakoğlu, former Senior Advisor to the Assistant Secretary for European and Eurasian Affairs at the U.S. Department State, said last May in Washington during a panel on Turkish-American relations.

I couldn't verify whether NATO also took advantage of the existence of the S-300 systems in Greece to learn and gain experience about the Russian technology. For sure, according to media reports, one country outside NATO, Israel, enjoyed this benefit.

The Israeli air force tested ways of defeating the S-300 defense system in April-May 2015 in a joint drill with Greece. A Reuters report said: "[The S-300's] activation allowed Israel's warplanes to test how the S-300's lock-on system works, gathering data on its powerful tracking radar and how it might be blinded or bluffed."

The report, referencing one defense source in the region, said that Greece allowed Israel to run such a test thanks to a request by the U.S..

Israel wanted to learn the ways to circumvent the S-300 defense umbrella because Iran had purchased them from Russia last year and successfully tested them earlier this year. No doubt this experience would be more than crucial in any possible Israeli operation against the Iranian nuclear assets.

Turkey's purchase of S-400s may provide the same crucial information for NATO.