By the mid-1930s the German military, as well as its counterparts in other countries, had come to see the main role of ground attack aircraft as the interdiction of logistics and materiel, a task in which targets were often poorly protected and less likely to be protected by strong, well-coordinated defences. For high-value, well-protected tactical targets dive bombers had become the conventional solution. However, the experience of the German Kondor Legion during the Spanish Civil War (1936–39) turned this idea on its head. Even though it was equipped with types unsuited to the role, such as the Henschel Hs 123 and cannon-armed versions of the Heinkel He 112, the Kondor Legion proved that ground attack aircraft were a very effective weapon. This led to support within the Luftwaffe for the creation of an aircraft dedicated to this role, and the Reichsluftministerium (RLM; "Reich Air Ministry") requested tenders for a specialized ground attack aircraft.
It was anticipated that the main source of damage to such an aircraft would be small arms fire from the ground, meaning that the plane had to be well-armored around its cockpit and engines. Similar protection was also needed in the canopy, in the form of 75 mm (2.95 in) thick armored glass. The aircraft was expected to be attacking in low-level, head-on strafing runs, so the cockpit had to be located as close as possible to the nose, in order to maximize the visibility of its targets. Another, non-operational, requirement severely hampered the designs: the RLM insisted that the new design be powered by engines that were not being used in existing aircraft, so that the type would not interfere with production of established types deemed essential to the war effort.
Only four companies were asked to submit tenders; three submissions followed and only two of these were considered worthy of consideration: One derived from an existing Focke-Wulf reconnaissance type, the Fw 189, and Henschel's all-new Hs 129.