Junkers Ju 87 with the Ju 87 A-0, the B-1s were returned discreetly to the Reich. The experience of the Spanish Civil War proved invaluable - air and ground crews perfected their skills, and equipment was evaluated under combat conditions. The Ju 87 had not been tested against numerous and well-coordinated fighter opposition; this lesson was learned later at great cost to the Stuka crews. All Stuka units were moved to Germany's eastern border in preparation for the invasion of Poland. On the morning of 15 August 1939, during a mass-formation dive-bombing demonstration for high-ranking commanders of the Luftwaffe at Neuhammer training grounds
Hugo Junkers communist activist, as Managing Director of what remained of his business. Hugo Junkers is mainly known in connection with aircraft bearing his name. These include some he reluctantly developed for the German Empire during World War I, later in minor association with Anthony Fokker, as well as civil aircraft designs during the "interwar period" produced by "Junkers Flugzeugwerke" (Junkers Aircraft Works). Junkers died in 1935. The earliest all-metal post-World War I aircraft designs of both Andrei Tupolev — with his Tupolev ANT-2 two-passenger small aircraft of 1924 — and William Bushnell Stout's initial all-metal design, the Stout ST twin-engine torpedo