Abstract: In recent times, autonomous and semi-autonomous unmanned aerial vehicles (UAVs) fleets have begun to generate a lot of research interest and demand from a variety of civilian applications. However, in order to successfully perform a variety of missions, fleets of UAVs require GPS signals, which unfortunately are unencrypted and uncertified. This facilitates the implementation of GPS spoofing attacks, in which an adversary mimics a real GPS signal and broadcasts it to a target drone in order to change its course and force it to land or crash. In this study, a GPS Spoofing detection mechanism is proposed to detect both single and multi-transmitter GPS spoofing attacks to prevent them from changing course or crashing. GPS Spoofing detection mechanism is based on comparing the distance calculated from their GPS coordinates between every two hive members and the distance obtained from pulsed radio UWB ranging between the same hive members. If the difference in distance is greater than a selected threshold, a GPS spoofing attack is declared detected. Finally, the case proves that GPS Spoofing detection mechanism is superior to the existing detection technology. It can detect GPS spoofs without modifying the original antenna or installing additional hardware. Moreover, it does not need complex calculation and communication overhead, thus reducing false positives and making the detection mechanism more reliable.