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 variants roles, a reconnaissance or bad-weather fighter, for example. Unlike the "Rüstsatz" field-kits, these modifications were permanent. The "Rüstsatz" kits were labelled with the letter "R" and a Roman numeral. "Rüstsatz" kits did not alter the aircraft type so a Bf 109 G-6 with "Rüstsatz" II (50 kg/110 lb bombs) remained a Bf 109 G-6 and not G-6/R2, which was a reconnaissance fighter with MW 50, as suggested by most publications. The "Umrüst-Bausatz", "Umbau" or "Rüstzustand" were identified with either an "/R" or "/U" suffix and an Arabic number, e.g. Bf 109 G-10/U4. Common "Rüstsatz" kits: Bf 109G: Common "Umrüst-Bausatz" ("Umbau")