public excitement as so-called "Rocket Rumble" and had a large long-lasting impact on later spaceflight pioneers, in particular on Wernher von Braun. The Great Depression ended these activities. Von Opel left Germany in 1930 and emigrated later to France and Switzerland. Starting in 1930, von Braun attended the Technical University of Berlin, where he assisted Oberth in liquid-fueled rocket motor tests. Von Braun was working on his doctorate when the Nazi Party gained power in Germany. An artillery captain, Walter Dornberger, arranged an Ordnance Department research grant for von Braun, who from then on worked next to Dornberger's existing solid-fuel rocket test site at Kummersdorf. Von Braun's thesis, Construction, Theoretical, and Experimental Solution to the Problem of the Liquid Propellant Rocket (dated 16 April 1934), was kept classified by the German Army and was not published until 1960. By the end of 1934, his group had successfully launched two rockets that reached heights of . At the time, many Germans were interested in American physicist Robert H. Goddard's research. Before 1939, German engineers and scientists occasionally contacted Goddard directly with technical questions. Von Braun used Goddard's plans from various journals and incorporated them into the building of the Aggregate (A) series of rockets, named for the German word for mechanism or mechanical system. After successes at Kummersdorf with the first two Aggregate series rockets, Braun and Walter Riedel began thinking of a much larger rocket in the summer of 1936, based on a projected thrust engine. In addition, Dornberger specified the military requirements needed to include a 1-ton payload, a range of 172 miles with a dispersion of 2 or 3 miles, and transportable using road vehicles. After the A-4 project was postponed due to unfavorable aerodynamic stability testing of the A-3 in July 1936, Braun specified the A-4 performance in 1937, and, after an "extensive" series of test firings of the A-5 scale test model, using a motor redesigned from the troublesome A-3 by Walter Thiel, A-4 design and construction was ordered 1938–39. During 28–30 September 1939, (English: The Day of Wisdom) conference met at Peenemünde to initiate the funding of university research to solve rocket problems. By late 1941, the Army Research Center at Peenemünde possessed the technologies essential to the success of the A-4. The four main technologies for the A-4 were large liquid-fuel rocket engines, supersonic aerodynamics, gyroscopic guidance and rudders in jet control. At the