The Messerschmitt Bf 109, interchangeably called the Me 109 (most often by Allied pilots and aircrew), was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid-1930s. It was one of the first truly modern fighters of the era, including such features as all-metal monocoque construction, a closed canopy, a retractable landing gear, and was powered by a liquid-cooled, inverted-V12 aero engine.