Syria's ability to defend its airspace against U.S.-led attacks depends largely on its surface-to-air missiles. Its air force is big but obsolete—the most numerous types by far are the MiG-21 and MiG-23—and some main air bases are in rebel-controlled areas. Mobile missiles belonging to the ground forces have likely been kept out of rebel hands.
The feared transfer of Russian Almaz-Antey S-300PMU-2 (SA-20 Gargoyle) long-range SAMs from Russia has not taken place, leaving Syria with at most eight batteries of the old S-200 (SA-5 Gammon)—a fixed-site weapon that, along with its radars, is vulnerable to destruction of enemy air-defenses operations. The same limitation applies to the 1960s-era V-750 (SA-2 Guideline).