Turkey, a member of NATO, tested the Russian-made S-400 air defense system on US-made F-16 jets during a drill in November 2019, Russia’s state media TASS has reported. The use of the S-400 against the F-16s was already reported last year, but the new details from Russian media appear to cement the claim and infer that something more was going on in those tests.Russia has an interest in knowing how well its air defense performs against US warplanes. Russia’s S-400 is the top tier of its numerous air defense systems. Some of these systems have been called into question due to mistakes. S-200s used by the Syrian regime shot down a Russian airplane by mistake in 2018. Iranian models of Russian systems have scored big in 2019 with the shoot-down of a US drone, but the Iranians also shot down a civilian jetliner in January. In Syria there are questions about the radar and reliability of the S-300s and Pantsir and other systems abilities to track modern drones and fifth generational jets. Russia’s Pantsirs were also destroyed by Turkish drones in battles in Idlib and Libya this year.It is therefore of great importance for Russia to know how the S-400 performed against a NATO member’s F-16s. What Turkey got out of this test is less clear now. Why would Ankara test the S-400 it bought from Russia against its own F-16s, unless it was at the behest of Moscow, wanting to see how it performed? The narrative last year was that Turkey merely wanted to test communications between the platforms so it didn’t shoot down its own jets.Russia’s TASS media only says that a source close to the Turkish defense industry told TASS that the S-400 was tested on the US-made F-16s. The S-400s are the center a controversy with Washington. By acquiring them for billions of dollars, Turkey has distanced itself from its traditional US ally and become a closer ally of Russia. The US administration has begged Turkey not to move toward Moscow, with one US senator even suggesting to buy the Russian S-400s from Turkey to please Ankara. What exactly the US would do with S-400s it doesn’t need is unclear – and it is unclear if Moscow would let the technology be floated on a barge over to the US to be picked apart by US engineers.Russia’s reasoning for bringing up the November tests this week is also unclear. Turkey got the S-400s in July 2019. It began to test them in November and they were supposed to be operational in April 2020. But they don’t seem to be operational yet. This raises questions about what was the overall point of Turkey spending billions on air defense it doesn’t need. For Russia, the point seems to be its desire to bring this up as part of an attempt to sink any questions about Turkey and the US working more closely.