The results of this investigation show the feasibility of designing a hybrid-electric unmanned aerial vehicle (UAV) that has low acoustic/visual signature and extended cruise flight endurance. The conceptual design is based on a small internal combustion engine that powers the cruise portion of the flight and an electric motor for loiter/intelligence, surveillance, and reconnaissance (ISR) portions. Relatively minor reductions in loiter mission duration produce a substantial increase in range. A decrease of 1 whr in the electric (loiter) energy onboard produces a gain of 13.3 whr in the gasoline (cruise) energy. These hybrid aircraft would allow extended range search-loiter-search missions, which are not possible with the existing electric UAVs.