When was the jet engine invented?

"Dr. Hans von Ohain and Sir Frank Whittle are both recognized as being the co-inventors of the jet engine. Each worked separately and knew nothing of the other's work. Hans von Ohain is considered the designer of the first operational turbojet engine. Frank Whittle was the first to register a patent for the turbojet engine in 1930. Hans von Ohain was granted a patent for his turbojet engine in 1936. However, Hans von Ohain's jet was the first to fly in 1939. Frank Whittle's jet first flew in in 1941."

In France, Maxime Guillaume was issued a patent for the use of an axial-flow turbojet engine to power an aircraft in 1921, but it is not clear that a working design for such an engine is part of the claims of the patent.

Hungarian mechanical engineer Albert Fonó filed a patent in Germany in 1928 for several jet engine designs, including a turbojet. The American Rocket Society reviewed Fonó's patents in 1960 and acknowledged him as the inventor of the jet engine.