The E-1 carried two 7 92 mm MG 17s above the engine & two more in the wings The E-1B became the first operational Bf 109 fighter bomber These were fitted with either one central bomb rack carrying one 250kg bomb or two under-wing bomb racks each carrying a 50kg bomb The E-3 was armed with the two MG 17s above the engine & one MG FF cannon in each wing The E-3 was replaced by the E-4 with many airframes being upgraded to E-4 standards starting at the beginning of the Battle of Britain which was different in some small details most notably by using the modified 20 mm MG-FF M wing cannon & having enhanced head armour for the pilot