Gunpowder was discovered long before WWII. It was used to propel bamboo rockets in China. The requirements of WWII called for heavy payloads and the use of more powerful fuels such as kerosine and liquid oxygen. Wernher von Braun's V2 rocket was a brilliant design which gave birth to modern day space travel. Militarily it was of little consequence. The V2 rockets that landed on London in 1944 were terrifying but little else.