If the US style of warfare is being used in the run up to Syria then you can bet that drones are flying all over the place trying to get a view on where key facilities and personnel are located.
What might slow down that effort? The Pantsir S1 anti air system. Read about the particulars here, but lets sum it up by saying it sports two 30mm cannons and 12 ready to launch missiles.
Add a few Russian Advisers, stir in lazy mission planning and we could see a few UAVs get knocked down.
But even more interesting is the fact that these weapons also have the capability to target cruise missiles...especially slow ones like the Tomahawk.
Sidenote: This is the same system that the Syrians credited with shooting down a Turkish RF-4E doing a recon mission along their coast.
