Aviation in World War II were struggling to re-equip with similarly modern types and to train up aircrew. Early German successes, with the notable assistance of the Junkers Ju 87 "Stuka" dive-bomber, overran Europe and left Britain open to attack. During the ensuing Battle of Britain, the British fighter squadrons had to quickly relearn the old tactical lessons from the first war. Initially the RAF fighters flew in a tight three-fighter arrowhead formation, soon changing to the looser four-aircraft arrangement which the Germans called the "finger-four." They soon also relearned the value of climbing above your opponent before attacking. At the same time, the development
Junkers J 2 1916 Hugo Junkers had come to the realization that the continued use of sheet electrical steel was no longer practical for aircraft construction, writing in his diary that: ""As a result of the first (J 1) and second (J 2) aircraft, one would ascertain that the aerodynamic efficiency was very good. We thought we" [the Junkers designers] "were over the hill. This, unfortunately, was not the case. We had to start again from the very beginning. The reason was that in spite of the favorable horizontal speed, the aircraft could not meet the military climb specifications...we had to develop an