The report by the IISS said about 170 sightings were reported between 20 and 26 November in 2024 over the three air bases, which are all used by the United States Air Force (USAF).
The drones entered the air bases at low altitude with their lights visible and departed at higher altitudes, the report continued.
There were swarms of up to 20 drones at a time and some were said to be flying low over runway approaches.
At the time, the USAF announced that “small unmanned aerial systems continue to be spotted” in the vicinity of the air bases.
A police helicopter sent to investigate reported a near-miss with what was later identified as a US F-15 fighter jet.
Despite the sightings, no verified footage of the drones around the bases has emerged – at least, not in the public domain.