Bye Aerospace of Denver, Colorado, is developing the Silent Guardian high-altitude long-endurance unmanned air vehicle. It is powered by a Williams International turbofan enabling it to reach its operating altitude quickly, before switching to electric motors to remain on station for extended periods. The UAV uses stored electric power, thin-film solar photovoltaic and other technologies to increase endurance and facilitate quiet operations. Silent Guardian is aimed at fulfilling persistent intelligence, surveillance and reconnaissance roles for commercial, defence and security applications. Detailed design work began in November 2013.