By the end of World War II, the Nazis were in a lot of trouble. Most of their weapons factories and airfields had been destroyed by combined Allied bombing, and morale was very low. It seemed imminent to the Nazi leadership that at this rate, the Third Reich's reign over much of Europe will end in no time. So, to balance the military books, the Germans turned to develop cutting edge and somewhat insane technologies to become technologically superior to their rivals. We all know about the Nazi research into Nuclear weapons and rocket technology. Although they couldn't reach anywhere with the former, in the latter case they were quite successful and made several short-range rockets though it saw no action in war. Many of these desperate attempts to excel in military technology helped us later on in space exploration too. This jetpack, on the other hand, didn't help us much.