Hopfner HA-11/33 , who later assumed the RLM designation WNF Wn 11, was an amphibious plane to the central hull and high-wing aircraft division developed by the Austrian company Hirtenberger Patronenfabrik (HP) in the early thirties and started production in series from the Wiener Neustädter Flughafenbetriebs GmbH.
Made for the civil aviation market, was later taken over by Heimwehr Flieger Korps, the then Austrian Air Force, then, after the ‘Anschluss, the German Luftwaffe to evaluate it.
In the early thirties, the Dr. Oetker, Austrian food company (currently known in Italy under the brand Cameo), commissioned to Hirtenberger Patronenfabrik (HP), a company active in the field of defense sector, a multi-role amphibious aircraft to allow you to move faster in various foreign subsidiaries of the company. The aviation division of HP, which would later become Wiener Neustädter Flughafenbetriebs, developed, designed by Theodor Hopfner, a twin-engine model in the central hull, characterized by a closed cockpit where they could find a place, in addition to the pilot, three passengers.
The prototype, marked A-141 and equipped with a pair of radial engines Siemens Halske Sh 14-A-4 160 hp (118 kW) each, was flown for the first time in the first half of 1933 from the surface of Lake Neusiedl.
After the acquisition of Germany was also planned a possible development, referred to as WNF Wn 11C, with enlarged five-seater cabin and a different engine system based on a pair of Hirth HM 508 D 240 PS (176.5 kW) , but not continued beyond the realization of a model for the wind tunnel.

In 1935 the aircraft was purchased by the Austrian Government on behalf of the Heimwehr, militia and former paramilitary organization, to train pilots destined for seaplanes of its air component (Heimwehr Flieger Korps) and re-registered OE-DGH.
With the annexation of Austria to Germany in 1938, generally known as the Anschluss, the entire Austrian aviation came under the control of the Reichsluftfahrtministerium (RLM) and its aircraft serving in the Luftwaffe. The construction company was redesignated Wiener-Neustädter-Flugzeugwerke GmbH (WNF), and the model in question was shown, in accordance with the designation system in force, WNF Wn 11 and again re-registered PH + IB.
The model sparked interest for its use as a training aircraft for pilots and it was sent to Travemünde for a series of tests in the operational field.

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