The development of jet propulsion and the aircraft gas turbine in Britain has two main lines. One began in 1926 when Dr A.A. Griffith, then of the Royal Aircraft Establishment (RAE), proposed the use of a gas turbine as an aircraft power plant. This line of development led to the Metropolitan-Vickers F2 jet engine and its derivatives. Our story began two years later in 1928 when Frank Whittle was a cadet at Cranwell. Each term, the cadets were required to write a thesis and in his fourth and final term Whittle chose as his subject “Future Developments in Aircraft Design”. He concluded that for very high speeds combined with long range, it would be necessary to fly at very great heights where low air density would greatly reduce resistance in proportion to speed. He was thinking in terms of speeds of 500 mph at heights where the, air density was less than one quarter of its sea level value.