The US-Russian relationship in Syria has been a frosty one with its share of risks. Russia's direct intervention in the Syrian civil war began with strikes on anti-Assad militias covertly supported by the West and on the CIA-provided weapons depots that supplied them. Those strikes exposed to the world what had previously been a black program. Russian fighters have routinely harassed US jets and unmanned aerial vehicles and invaded NATO airspace - a pattern that culminated in the downing of a Russian warplane over Turkish soil in mid-2015. Meanwhile, Syrian insurgents have been filmed destroying Russian armour and helicopters using sophisticated US weaponry.