Actually, the first designed-jet was built by 1910 courtesy of a Rumanian- Henri Coanda and was displayed in Paris. Coanda, unfortunately, had an accident with his plane which was a thermal-type (turbine driven by internal piston engine) and it was wrecked before it could fly and make history. WW1 could have had jet biplanes as reality, but neither the Germans nor the Allies expressed any interest from 1914-18. But during the 1930s Britain and Germany both were working on turbojet engines. It was a race between Pabst von Ohain in Germany and Frank Whittle in Britain. While Whittle made it to the patent office first by months, he failed to get a British jet to fly until during WW2. Germany's He-178 V1 took a hop on Aug 24, 1939 and then a flight on Aug 27, 1939... a few days before WW2. The V1 hit 403 mph and the V2 was expected to break 435 mph- but they were rejected by the RLM and Luftwaffe due to no requirement. The Luftwaffe already possessed the world's best fighter in the Me Bf 109E-4 and the Fw-190 was under development as well as Messerschmitt's jet 262. Heinkel was out of favor with the Nazis, so even though he flew the first jet and had the first designed jet by 1941 (the He-280 with ejection seat and to be armed with 3x 20mm MG-151/20s in the nose), he was rejected. Messerschmitt eventually had the 262 in operation in 1944 and Heinkel sadly just barely got his He-162 into the fight in April 1945. The argument has always been "What IF" the Germans would have developed the Heinkel jets and got them operational by 1943??? That is a myth as the jet engines were never ready by 1943 and even when operational lacked strategic metals, so service life was initially 10 hours!!! The Germans developed synthetic parts and lubricants to the point that the 1945 Jumo 004s could take 25-30 hrs. Whereas the Me-262 killed 509 Allied aircraft, the He-162 got 4 kills in 3 weeks before the war ended. Heinkel's jet bomber He-343 was also put on hold and into storage while Arado flew the Ar-234 first jet bomber and recon aircraft. By 1945, the Ar-234C was the first 4-engined type followed by the Ju-287...

http://www.warbirdsresourcegroup.org/LRG/images/he178-2.jpg http://www.militaryfactory.com/aircraft/imgs/he178.jpg