The Henschel Hs 129 was a World War II ground-attack aircraft fielded by the German Luftwaffe. Its nickname, the Panzerknacker (tank cracker), is a deliberate pun-in German, it also means "safe cracker." In combat service the Hs 129 lacked a sufficient chance to prove itself; the aircraft was produced in relatively small numbers and deployed during a time when the Luftwaffe was unable to protect them from attack. "The Spanish Civil War of 1936-1939 was politically the opening stage of an overall world conflagration. From a military point of view, the conflict was a unique chance for the involved parties to experiment with the latest war doctrines, particularly the large-scale use of air power. Spain was also an ideal testing ground for a large variety of innovative warfare technologies, including combat aircraft. It was also in Spain that the need for close air-support for one's own advancing or retreating combat troops had first emerged. The task of destroying fixed or slowly moving smaller targets such as ships, for example, was solved by employing the dive-bombing technique with its pinpoint accuracy, carried out by the Sturzkampfflugzeug, or Stuka - as the famous, or infamous, Junkers Ju 87 is widely known. However, the neutralization of fast and manoeuvrable small objects - tanks and other armoured or soft-skinned vehicles, as well as groups of mounted enemy troops - had been only partially resolved by the use of biplanes of older types - for example, the Heinkel He 51, or the Henschel Hs 123 (the initial Stuka) - as ground attack aircraft. As proven in Spain, these obsolescent airplanes were not fully suited to the task assigned to them, being rather slow, lightly armed and non-armoured, thus vulnerable to ground fire. The experience in the Spanish war theatre highlighted the need for a well protected and heavily armed specialized Schlachtflugzeug (ground attack aircraft). The existence of such a dedicated aircraft type was fully justified by the apparent necessities of the modern, fast-changing battlefield with flexible front lines, in contrast to the mostly fixed trench warfare, which characterized the 'Great War'.