During the latter half of 1930s, influenced by the experiences of German Condor Legion during the Spanish Civil War, the Reichsluftfahrtministerium (RLM; "Reich Aviation Ministry") sought a new ground-attack aircraft.

While Henschel faced competition to fulfil the requirement in the form of the Focke-Wulf Fw 189, the Hs 129 was both smaller and cheaper, and thus continued to hold the RLM's favour.

Production of the type peaked in 1943 and was terminated entirely in September 1944 in response to Nazi Germany's declining military position, although use of the HS 129 continued into the closing months of the conflict.

[2] By the mid-1930s, the German military, as well as its counterparts in other countries, had identified the importance of ground-attack aircraft for the interdiction of logistics and materiel, a task in which targets were often poorly protected and less likely to have strong or well-coordinated defences.

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 Condor Legion proved that ground-attack aircraft were effective in actual combat.

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.

[4] Of these, Gotha opted to not respond at all while the Hamburger Flugzeugbau offered their P-40 project, a development of their two seat Ha 141, however, the ground attack version was considered to be too unconventional and was eliminated.

[3] On 1 October 1937, the RLM issued a pair of development contracts for the two other submissions, which had been determined to superior: one was derived from an existing Focke-Wulf reconnaissance type, the Fw 189, while the other was produced by Henschel.

It was designed around a single large "bathtub" of steel sheeting that made up the entire nose area of the aircraft, completely enclosing the pilot up to head level.

To improve the armor's ability to deflect bullets, the fuselage sides were angled in, forming a triangular shape, resulting in almost no room to move at shoulder level.

[7] The controls proved to be almost inoperable as speed increased and in testing, the V2 prototype flew into the ground from a short dive on 5 January 1940 because the stick forces were too high for the pilot to pull out.

[7] Even prior to the delivery of the first A-1s, the aircraft already being redesigned in response to an instruction from the RLM to adopt French Gnome-Rhône 14M radial engines, which were captured in some number when France fell and continued to be produced under German occupation.

[12] Although reviewing pilots were more satisfied with the aircraft's performance, complaints continued to be filed about the high stick forces as well as the poor visibility from the canopy.

[12] Accordingly, new electronically-actuated trim tabs and a redesign canopy with more extensive glazing was installed on the HS 129 B-0, along with a special Revi V12/C sight that was mounted externally just forward of the windscreen.

[12] Initially, the two models were quite similar, although some difference were apparent in terms of the positioning of the radio apparatus and the presence of exposed blast troughs for the guns on the B-1.

They were promptly assigned to the Eastern Front (to Crimea) in the middle of May 1942 and in June they received a new weapon, the 30 mm (1.2 in) MK 101 cannon with armor-piercing ammunition in a centerline pod.

An autoloader system, with 12 rounds in a rotary magazine, was fitted in the empty space behind the cockpit, within the rear half of the wing root area.

[18] While deliveries commenced to actual frontline units, around 25 B-3s are believed to have been completed prior to the production line being permanently shut down in September (a small number were reportedly also created by converting B-2 aircraft).

[citation needed] To address the poor performance of the aircraft, plans had been under way for some time to fit the aircraft with newer versions of the Italian Isotta-Fraschini Delta air-cooled inverted V12 inline engine that delivered 850 hp (625 kW) and weighed some 510 kg (1,120 lb) apiece, providing more power than the Argus As 411 engine of similar configuration and lighter (385 kg) weight.