The Messerschmitt Bf 109, often called Me 109, 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 true modern fighters of the era, including such features as an all-metal monocoque construction, a closed canopy, a retractable landing gear, and was powered by a liquid-cooled, inverted-V12 aero engine. The Bf 109 first saw operational service during the Spanish Civil War and was still in service at the dawn of the jet age at the end of World War II, during which time it was the backbone of the Luftwaffe's fighter force. From the end of 1941 the Bf 109 was supplemented by the Focke-Wulf Fw 190.