The first jet engines were developed between 1939 and 1941 in Germany
[1] and Great Britain.
[2] The early experimental flights were accomplished by burning hydrogen,
gasoline, diesel, and kerosene for illumination. Eventually, only lamp kerosene and car gasoline were used in the final prototype flights. However, gasoline presented a major problem: at the time, it had a low flashpoint
[3] which made fires much more likely in case of accident.