Structural improvements to the A1 led to an improved defensive armament and changes to the wing. The result was the Ju88A-4 which entered mass-production on a large scale and became the Luftwaffe's standard bomber. It was the basis for all further development of the Ju 88 as a bomber, ground-attack and reconnaissance aircraft. The A-4 is one of the most prolific version of the Ju 88. Compared to its predecessors, it was extensively better armoured to protect the crew, had a more powerful engine and an uprated defensive armament.
The first major deployment of the new aircraft was with KG 51 (Combat Wing 51) during the invasion of the Soviet Union on 22 June 1942. The Ju88A-4 was used in all theatres of war and was continuously improved. As well as aerodynamic improvements, engine performance was increased and a greater payload became available. Thus, the Ju88A-4 could carry up to 4 SC500 bombs intoaction. The exact number of Ju88's built is difficult to determine. In all thereabout 15,000 were built.