The Messerschmitt Bf 109 is a German World War II fighter aircraft that was, along with the Focke-Wulf Fw 190, the backbone of the Luftwaffe's fighter force. The Bf 109 first saw operational service in 1937 during the Spanish Civil War and was still in service at the end of World War II in 1945. It was one of the most advanced fighters when it first appeared, with an all-metal monocoque construction, a closed canopy, and retractable landing gear. It was powered by a liquid-cooled, inverted-V12 aero engine. It was called the Me 109 by Allied aircrew and some German aces, even though this was not the official German designation.

Early 1940 began with design improvements with the Bf-109 as well as the addition of the new DB 601E engine. The under-wing radiators were reduced in size and recessed; cutting down on drag as well as some other changes. A redesigned cowling and a repositioning of the air intake for the supercharger along with a larger propeller hub also helped reduce drag. The overall airscrew diameter was reduced by 4 inches by using wider blades. The most noticeable change was the removal of the tail-plane bracing struts. The result of this program was the Bf 109F