The first German mass produced 109 fighter was the Bf-109E that has been mistakenly referred to as the Me-109. The Bf is the designator for the Bayerische Flugzeugwerke (BFW) (Bavarian Aircraft Works) that produced the original aircraft. In 1938 Messerschmitt took over BFW but throughout WWII German handbooks and documents referred to the aircraft as the Bf-109. By the end of 1939 the Bf-109E (Emil) had replaced all other 109 variants and equipped 13 Gruppens with 40 aircraft each. The Bf-109 was the main single-engine aircraft until the Fw-190 came along.
JG 77 (Jagdgeschwader 77) took part in the Battle of Britain, Norway, North Africa, Italy, Greece, Crete and the Eastern Front. In April 1940 JG 77 helped with the invasion of Norway, in May the invasion of France. I./JG 77 remained in France to take part in the Battle of Britain while the other Gruppens were sent elsewhere. During the summer of 1940 I./JG 77 aircraft wore lightning bolts (Blitz or plural Blitzen) the length of the fuselage sides. In November 1940 I./JG 77 became Stab IV./JG 51.