On this day in 1931, the United States Navy tested the XOP-1 Giro, the first ever rotary wing aircraft at NAS Anacostia in Washington, D.C.

Neither airplane nor helicopter, the XOP-1 was an autogiro. The design had a standard aircraft fuselage and powerplant, with a standard tail. However, it sported short, stubby wings, angled up at the wingtips. Above the cockpit was the rotor, consisting of three blades. The engine usually drove a standard propellor, on a vertical plane, in front of the aircraft. However, the engine could be geared to the horizontal rotor during takeoff or landing. The horizontal rotor, while in flight, did not draw energy from the engine but rather generated lift from airspeed. A minimum speed of 30 mph was needed to keep the aircraft in flight. Thus, in moderate winds, the aircraft could behave like a helicopter, except that it could not hover. (Photo: Smithsonian Institution)