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. Sir Frank Whittle was an English aviation engineer and pilot, the son of a mechanic, Frank Whittle joined the Royal Air Force or RAF as an apprentice. He joined an RAF fighter squadron in 1928 and became a test pilot in 1931. The young RAF officer was only 22 when he first thought to use a gas turbine engine to power an airplane. While often regarded as the father of modern jet propulsion systems, the young Frank Whittle tried without success to obtain official support for study and development of his ideas. He had to persist his research on his own initiative and received his first patent on turbojet propulsion in January 1930. With private financial support, he began construction of his first engine in 1935. This engine, which had a single-stage centrifugal compressor coupled to a single-stage turbine, was successfully bench tested in April 1937; it was only a laboratory test rig, never intended for use in an aircraft, but it did demonstrate the feasibility of the turbojet concept. The modern turbojet engine used in many British and American aircraft is based on the prototype that Frank Whittle invented.