This study evaluated the feasibility of swapping a system of small multi-rotor unmanned aerial systems during flight for persistent perimeter surveillance. The systems engineering processes, such as requirement analysis and functional analysis, were followed by designing the overall concept of system and identifying high-level requirements for it. The research also included system prototyping. The developed system prototype consisted of three COTS products: multiple quadcopters, a single router, and a laptop running Python code. Quadcopters were programmed to fly in different predefined patterns over the Military Operation at Urban Environment Training site at Impossible City, CA, and McMillan Field at Camp Roberts, CA. Videos were recorded during the tests. While one quadcopter was flying, the remaining two stayed on stand-by. Once the airborne quadcopter depleted its battery life to the predetermined level, one of the standby quadcopters was activated as a replacement. The process can be repeated continuously, assuring an uninterrupted video stream. By monitoring the battery level and autonomously swapping quadcopters, the system showed that endurance can exceed the capability of a single quadcopter and possibly perform 24/7 persistent surveillance, or until the system fails mechanically.