AbstractThe hybrid aerial underwater vehicle (HAUV) merges the best of unmanned aerial vehicle (UAV) and unmanned underwater vehicle into one platform makes it possible to operate in both the air and water. Various possible applications of HAUV have aroused much research on it. However, the underwater endurance and operation depth of current HAUVs are still limited. This hinders the application and popularization of HAUV in rugged environments. This paper presented the design, fabrication, and testing of a novel concept HAUV, Nezha III. It is featured by its piston‐driven underwater glide strategy and combination of an underwater glider and fixed‐wing vertical takeoff and landing aircraft. In‐depth design and evaluation of the amphibious wings with tradeoffs between aerodynamic and hydrodynamic performance in both fluids was conducted. The vehicle prototype was built, and field experiments, including domain transitions and underwater operations, were conducted in Qiandao Lake, China. Due to the experiment site constraints, the computational fluid dynamics technique evaluated horizontal flight performance with fixed wings. The experimental results show that the prototype can realize rotor flight and stable domain transitions. Moreover, this piston‐driven underwater glide strategy extended the HAUV's underwater endurance over 24 h and operational depth to 25.5 m. To the best of our knowledge, Nezha III possesses the most extended underwater endurance among existing HAUVs.