Plans were first drawn up in April 1939, and the original design was very different from the aircraft that eventually entered service, with wing root-mounted engines, rather than podded ones, when submitted in June 1939. The progression of the original design was delayed greatly by technical issues involving the new jet engine. Because the engines were slow to arrive, Messerschmitt moved the engines from the wing roots to underwing pods, allowing them to be changed more readily if needed; this would turn out to be important, both for availability and maintenance. Since the BMW 003 jets proved heavier than anticipated, the wing was swept slightly, by 18.5°, to accommodate a change in the center of gravity. Funding for the jet engine program was also initially lacking as many high-ranking officials thought the war could easily be won with conventional aircraft. Among those were Hermann Göring, head of the Luftwaffe, who cut the engine development program to just 35 engineers in February 1940 (the month before the first wooden mock-up was completed); Willy Messerschmitt, who desired to maintain mass production of the piston-powered, 1935-origin Bf 109 and the projected Me 209; and Major General Adolf Galland, who had initially supported Messerschmitt through the early development years, flying the Me 262 himself on 22 April 1943. By that time, problems with engine development had slowed production of the aircraft considerably. One particularly acute problem arose with the lack of an alloy with a melting point high enough to endure the high temperatures involved, a problem that by the end of the war had not been adequately resolved. The aircraft made its first successful flight entirely on jet power on 18 July 1942, powered by a pair of Jumo 004 engines, after a November 1941 flight (with BMW 003s) ended in a double flameout.