The Heinkel He 51 was a German single-seat biplane Fighter aircraft, developed from the earlier Heinkel He 49. Sea-plane and ground-attack variants were also developed.
In 1931, Heinkel recruited Walter and Siegfried Günter, and they designed the He 49. Whilst this was officially an advanced trainer aircraft, it was also a fighter. The first prototype of the He 49, the He 49a, flew in 1932 and was followed by two more prototypes, the He 49b with a longer fuselage,and the He 49c with a revised engine. The He 49 was ordered into production as the He 51 by the still secret Luftwaffe, and testing began in 1933. The Heinkel He 51 was intended to replace the Arado Ar 65, but ended up serving side-by-side with the Arado Ar 68. Though the He-51 was outdated the day it entered service, it was the best fighter Germany had at the time.
Though the initial order for He 51A-1s was only 75, Heinkel was unused to such an order and many were built under licence by Ago, Erla, Arado and Freseler, which were also fast tooling for their own designs. In March 1935 the Luftwaffe was publicly announced, and JG1 "Richthofen" fighter squadron was combat—ready at Déberitz with its new Heinkels, In November 1936. 36 He 51A—1s went to Spain with the Legion Kondor, giving a sufficiently good showing for the Nationalists to buy at least 30 from Heinkel. There followed a total of 50 of various He 51B seaplane versions, the 38 B-2s being for service aboard cruisers. The final batch comprised 79 C-1 ground attack fighters. of which 28 served in Spain. The He 51 was still in active service_in September 1939, operating in the close-suppon role in Poland, and remained as an advanced trainer until 1943, by which time the wheel spats had almost always been removed.
As well as using He 51s in anger in the Spanish Civil War, Germany also took this opportunity to use the battleground as a testing site for future weapons and vehicles they would later use against Europe.
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