Messerschmitt Bf 109 11 July 1938 when Erhard Milch finally allowed Willy Messerschmitt to acquire the company. All Messerschmitt aircraft that originated after that date, such as the Me 210, were to carry the "Me" designation. Despite regulations by the RLM, wartime documents from Messerschmitt AG, RLM and "Luftwaffe" loss and strength reports continued to use both designations, sometimes even on the same page. All extant airframes bear the official "Bf 109" designation on their identification plates, including the final K-4 models. The aircraft was often referred to by the folk-designation, 'Me 109', particularly by the Allies. The aircraft was often nicknamed "Messer"
Messerschmitt Bf 109 by its operators and opponents alike; the name was not only an abbreviation of the manufacturer, but also the German word for "knife". In Finland, the Bf 109 was known as "Mersu", although this was originally the Finnish nickname for Mercedes-Benz cars. Soviet aviators nicknamed the Bf 109 "the skinny one" (худо́й, "khudoy"), for its sleek appearance compared, for example, to the more robust Fw 190. The names "Anton", "Berta", "Caesar", "Dora", "Emil", "Friedrich", "Gustav", and "Kurfürst" were derived from the variant's official letter designation (e.g. Bf 109G – "Gustav"), based on the German spelling alphabet of World War II,