In 1939 the German air ministry issued a "Bomber B" requirement for a replacement for the Heinkel He 111 and Junkers Ju 86. Junkers proposed the Ju 288 as an advanced design. However, the Ju 288 was delayed and the Ju 188 was more conventional.
The first prototype of the Junkers Ju 188 was a Junkers Ju 88E that was modified. The wings had a pointed tip and were longer. The empennage was changed as well. It could have either Junkers Jumo 213s or BMW 801s engines installed. The BMWs were available in greater quantities so they were installed.
The cockpit was encased in glass. The dorsal turret was located above the cockpit.
The German air ministry wanted the Ju 188 to have interchangeable engines. It would be able to use the Jumo 213 or BMW 801 depending on availability.
The engines had MW50 methanol-water injection to increase performance.
In the reconnaissance version the bomb bay was converted to carry a fuel tank.
The wings had extended wingtips to increase performance.